Race gas back fire

Related:
Create New Tag

9/4/2018 8:09 PM

Bike is my son's stock 2018 yz250f. He likes to run vp t4 for the "extra" power out of turns. The problem is a wicked back fire after jumps. It always happens after he let's off the gas right after leaving the face of a jump. With pump gas the bike runs fine. We messed with different settings with the gytr programmer but usually made the problem worse, that and I don't understand how to use the timing part for performance. Right now he likes the stock setting. Any ideas on using the programmer to eliminate the back fire. Thanks

|

9/4/2018 11:57 PM
Edited Date/Time: 9/4/2018 11:59 PM

you are likely better off with the pump gas you were using, and it is unlikely it has more power with t4 unless the bike was pinging on pump gas and has a knock sensor. if you use the race gas, you should try advancing the timing.

|

9/5/2018 3:06 AM

That fuel is supposed to be a stock replacement. It shouldn't cause this problem. Are you running all "0's" on the programmer? We have ran 110, 100, and regular 93 in our 15 and 16 and not experienced a backfire...

Are you sure of the age on the T4?

|

2020 YZ450F
2018 KTM 450SXF FE
2016 YZ250F 2008 CRF450R
2015 YZ250F 2008 CRF250R
2001 CR250R
2010 YZ250 2012 CRF150R
2009 YZ125 2010 KX109.5
SSR Motorsports Dealer YCF Motorcycles
TAGMX Suspension & Graphics! www.tagmxsuspension.com https://www.liquidskinzdesign.com/



9/5/2018 3:53 AM

Did you try having a shop map the bike for that gas? Its a little different than doing it yourself.

|

9/5/2018 7:42 AM

Yes running all 0s on the programmer.
I have checked for leaks in the exhaust system and replaced the exhaust gasket at the last rebuild. We also installed a quick turn throttle tube.

|

9/5/2018 12:55 PM

Remember that the higher the octane the slower it burns and thus you will experience more exhaust popping using higher octane fuels in an engine that does not need them.

Paw Paw

|

9/5/2018 3:40 PM
Edited Date/Time: 9/5/2018 3:41 PM

Paw Paw 271 wrote:

Remember that the higher the octane the slower it burns and thus you will experience more exhaust popping using higher octane ...more

and this is exactly why the timing can be advanced which will also reduce or possibly even eliminate the backfire.

.

|

9/5/2018 5:56 PM

|

9/5/2018 6:22 PM

So do I advance timing on top or bottom or all over. Paw paw 271 yea I understand the whole not needing race gas in a stock motor but he is convinced he is faster with it, and his lap times show it. I think alot of it is in his head. He got moved up to B class this year after his results this year in the amateurs and he thinks he needs it to hang with the fast guys. I thought about just starting to cut his gas with pump gas to see if his lap times go down, this done without him knowing.

|

9/5/2018 7:37 PM
Edited Date/Time: 9/5/2018 7:45 PM

redduk wrote:

So do I advance timing on top or bottom or all over. Paw paw 271 yea I understand the whole not needing race gas in a stock ...more

it's in his head. it's the placebo affect. any pro on an identical bike with pump gas will smoke your son, which means his engine has way more power than he can use in stock form and he doesn't need any more, he simply needs more experience but many kids don't want to hear that or simply don't believe it.

if there is an option to advance it individually on the top and the bottom, you can do several different tests, but you could try advancing it just on the bottom first. load increases the potential for pinging. there is far less load on an engine in the higher rpm range. advancing timing increases power and throttle response, up until the timing is advance too far, at which point performance will be reduced. Also, the more the timing is advanced, the more fuel is occasionally required although it is a fairly small amount.

also, i would do blind tests so he has no idea what you are doing. all tests need to be done at least twice to have any type of meaningful results.

the ideal thing to do would be to simply put it on a dyno then do the changes on the dyno. you can also test 91 pump gas vs race gas this way. it costs $125.00 for an hour total on the dyno where i am.

|

9/6/2018 4:53 AM

Not going to argue the whole race gas theory but many people have stated they feel a difference with t4e.


I run a mix of 93 and 110 in my yz450. Mostly just to help keep the gas fresh.

|

9/6/2018 9:30 AM

There is a long list of reasons to run race fuel over pump gas, in your case making more power on a stock bike is completely valid. T4 is designed as a pour in replacement for pump 93, my guess is the popping has more to do with TPS from the dealer then the change in fuel, especially because you said it pops on pump gas. That being said T4/T4e is a bit higher octane (100 R+M/2) and slightly oxygenated. Depending on how the bike is tuned from the factory, which varies by manufacturer and year, on a stock application you should see more of a gain by advancing ignition timing and richinging up FI with T4. Exactly how much of each for different bikes/years/fuels and mods is part of what keeps guys like Tokyo Mods and Twisted Development in business charging $100-250 to tune a stock ECU. Check out the map pictured on a GYTR tuner- I would start by increasing FI across the board to address the decel backfire. I would try +2 across the bottom two row and +3 across the top on FI leaving IG alone, then mess with IG. The IG map is off a 2017 GYTR map from Yamaha.

Photo

|

9/6/2018 1:27 PM

Thanks for all the help, gives me a direction to go this weekend.

|

9/6/2018 7:16 PM
Edited Date/Time: 9/6/2018 8:02 PM

There is a long list of reasons to run pump gas over race gas in many high perf engines. One type of fuel does not work best in every engine, which is one reason that vp makes SEVENTY THREE different types of race gas, and in general, the higher the octane content of a fuel, the LESS power it will make in an engine if all else remains the same with the engine and the fuel. It has always been that way and still is today, and if you call vp racing fuel and ask one of their techs, they will tell you the exact same thing.

Here is a number you can reach a vp tech at.

(951) 696-5100

VP FUEL LIST

https://vpracingfuels.com/master-fuel-table/

Also, their is a large discrepancie between T4's RVP rating on VP's site. The main fuel page lists it as 6.7 while the specific spec page for it lists it as 8.54, therefore, it is always best to call a fuel mfg to determine the correct specs for a fuel if you need them.


If you can get shell v power 93 or 95 octane where you are you could try that also.

If you want to use race gas to get more power. i would call vp and ask them about c10 and u4.4 and the t4 to see what they say and which one they think might be best for your app.



|

9/7/2018 7:03 AM
Edited Date/Time: 9/7/2018 7:11 AM

Barnett468- I agree with you on most of that, except for there being a long list of reasons to run pump gas over race gas in many high performance engines. I’d say there is a very short list mostly centered around price, which is debated when it comes to long term results of running low quality fuel. There is a race fuel from VP for every high performance engine that will outperform pump gas in every aspect. Your octane statement is generally correct, although misleading in this case. There are a large number of fuel blends from VP that cater to wide variety of applications. Check out MXA's “hierarchy of race fuels”, they provide a pretty good breakdown of the most popular motocross fuels, and yes there are a few more from VP outside of this list that work well in motocross applications. Vital also ran a test of with dyno results. Calling VP Racing Fuels and asking what will work best for you is definitely the best course of action. I like the guys at the VP Southeast office, their number is 954-565-7670.

https://motocrossactionmag.com/racers-guide-to-the-hierarchy-of-motocross-racing-fuels/

https://www.vitalmx.com/product/feature/Tested-VP-Fuels-Comprison,3212

|

9/7/2018 8:38 AM
Edited Date/Time: 9/7/2018 9:01 AM

ZB93 wrote:

Barnett468- I agree with you on most of that, except for there being a long list of reasons to run pump gas over race gas in ...more

Well I was a pro mx racer in the mid to late 70's and occasionally raced against peopke like galon mosier, warren reid, jeff jennings and so on,and everyone used pump gas then, but of course the octane rating was higher. I was in charge of the atv department in r & d at kawi motors in the mid 80's and raced pro 3 and 4 wheelers and used c12 then because of the higher compression. The factory mx race team used pump gas and jeff ward won several championships with it. Team green also used pump gas and won far more championships with it than any other mfg, so i have a fair amount of experience with race gas and again can say from my first hand experience experience that it will not make a hill of beans of difference to any non pro mx rider if his bike isn't pinging, all they have to do is ride faster because it is impossible for them to use all the power the bike has anyway. It really is that simple. It is also completely pointless to use it unless the bike is also timed and jetted for it. In fact, in some cases, one can get a little more power and a little better throttle response from their bike by simply altering the stock timing and fuel curves.

I also ran sunoco 100 and 105 a few times in the 70's and 80's. .

I also raced the expert vintage 125, 250, open, and over 40 class in 93 and holeshot more races and won more trophies at the years end western regional awards than any other person in vintage racing history, and i did that all with pump gas.

I am hopefully going to get my vintage bike on the dyno in few weeks and i am going to dyno it with a few before and after changes and one of them will be pump gas vs a mix of pump gas and vp's street blaze. granted, their street blaze isn't the best they have but it is oxygenated so i will see what happens, plus it is only around $8.50 a gallon.

I forgot to mention that i nearly holeshot a race at the othg race at perris raceway a few weeks ago on my 38 year old non power valve yz250 with a seriously dented pipe and they all have newer $9,000.00 4 strokes, and most were 450's. I also beat half of them but of course it wasn't in the pro class and i used pump gas with 25% sunoco 100 but i used the sunoco because my bike was pinging horrendously bad at the vintage race 2 weeks before that, however, i found an air leak after that race so that may have contributed to the problem.

|

9/7/2018 9:16 AM

Roger that! I can definitely appreciate your background and experience, and without listing mine, my statement from first hand experience stands that running race fuel will absolutely make a difference on the track to non-pro riders, the same way any performance part in their program will. It's why the vast majority of competitive amatures, especially ones on stock bikes in limited classes that I figured might be the case of this post, run VP.

|

9/7/2018 9:27 AM

If you have the money race gas is for sure better. Youre looking at what? 14.5:1 compression ratio on these bikes these days? You basically want diesel at 16:1. 2 strokes are really low. I think a yz250 is 9 or 9.5 to 1 and it required 95 octane fuel. These high compression 4 strokes benefit from clean consistent gas. Pump gas these days is loaded with ethanol and lower octanes than ever before.

With the right map and race gas youll only see benefits in performance. Only drawback is a lighter wallet

|

9/7/2018 6:23 PM
Edited Date/Time: 9/7/2018 6:34 PM

kb228 wrote:

If you have the money race gas is for sure better. Youre looking at what? 14.5:1 compression ratio on these bikes these days? ...more

"14.5:1 compression ratio on these bikes these days?"

2018 kawi 450 is 12.8 and the 2018 husky 450 is 12.6, however, that is irrelevant because those are static/uncorrected figures and the main number that determines what octane level is needed for an engine is the dynamic compression number. You can have an engine with 12.1 static compression and 9.0 dynamic compression, then change the cam to one with longer intake duration and keep the other cam specs the same and it will have less dynamic compression which will require less octane and vice versa. Another factor that determines an engines octane requirement is load. The greater the load, the higher the octane requirement. Load can be reduced by installing numerically higher final drive gears. Another factor is combustion chamber design. Some designs burn the fuel more quickly and engines with "quick burn" combustion chambers require less timing or more octane to prevent the engine from pinging. Some other factors that determine octane needs are ambient air temp, humidity, air density/elevation and so on. The kawi race mechanics had thick notebooks of atmospheric stats and jetting specs they gathered throughout the years at different races and would use those as a guide at each track so they wouldn't have to waste time starting from scratch when jetting for the different tracks.


"These high compression 4 strokes benefit from clean consistent gas."

In general, every engine can benefit from consistent gas, and contrary to many peoples incorrect belief, pump gas is consistent to the point that and difference in it throughout the year is insignificant. The main exceptions to that are states like california and some parts of arizona that oxygenate the fuel and add ethanol to it during certain parts of the year.


"Pump gas these days is loaded with ethanol..."

There is nothing inherently "wrong" or "bad" about ethanol other than it can attract water. Ethanol is alcohol, and the fastest cars in the world run straight alcohol, not gasoline.


"With the right map and race gas youll only see benefits in performance"

You are correct and I have already stated this, but you and some others keep missing that fact.



|

9/7/2018 6:36 PM
Edited Date/Time: 9/7/2018 6:47 PM

ZB93 wrote:

Roger that! I can definitely appreciate your background and experience, and without listing mine, my statement from first hand ...more

My guess is that you and the majority of these other riders also all changed your timing and fuel settings to achieve more power etc. If this is the case, it simply proves my point.

Also, eddie warren won the amateur championship at loretta lynns around 1984. I went with the race team to an ama 250 national they had the next week that they signed eddie up for. He got lapped by the leaders on a course that was over 2 minutes long and all the race gas in the world would not have prevented that.

Skill is far more important than race gas providing the engine isn't going to blow up from detonation. It's really that simple.

|

9/7/2018 8:13 PM

ZB93 wrote:

Roger that! I can definitely appreciate your background and experience, and without listing mine, my statement from first hand ...more

barnett468 wrote:

My guess is that you and the majority of these other riders also all changed your timing and fuel settings to achieve more ...more

Your points aren’t invalid, but remember that pump gas back then was of decent quality with less additives. Pump gas today is crap.

|

9/7/2018 8:31 PM

Not sure how this thread got from helping someone out with a backfire issue, to debating weather skill is more important than adding power to the bike... but that seems to be the trend on a lot of threads. In any event, I feel compelled to comment on statements about fuel based on what I know to be true, which is rooted in a fairly extensive knowledge and experience with racing fuel.

Pump gas quality and consistency has degraded significantly over the years. By any racer's standards, pump gas is not consistent in any state. The inconsistencies in hydrocarbon quality, energy, specific gravity, rvp, ethanol content, water content and actual octane are significant enough to effect engine performance and tuning, both on a dyno and on the track.

Pump gas is loaded with ethanol. While it is not inherently bad in some applications, it is most certainly inherently bad in small displacement 4 stroke and 2 stroke engines, there is a plethora of evidence on this. The ethanol found in pump gas is not the alcohol that the world's fastest cars run. There are many forms and byproducts of alcohol that differ drastically, which are often referred to as alcohol.

There is a measurable gain in throttle response, horsepower and torque to be had by running the correct race fuel in modern day 2 and 4 stroke bikes with stock ignition timing and fuel/carb settings. These gains are amplified when you can tune for the change in fuel, the same way you would when changing any engine component.

I feel the "save your money just twist the throttle more" argument is counter productive in most of these discussions. Would a rider benefit more from spending $1000 training for a few days at a world renowned facility, or on a new exhaust system that had concrete evidence of a hp gain? I think you could form a solid argument for the training over the exhaust in many cases. That doesn't change the fact that the exhaust system will add power to the bike over the stock system.

|

9/7/2018 8:40 PM

omalley wrote:

Your points aren’t invalid, but remember that pump gas back then was of decent quality with less additives. Pump gas today is ...more

ummm...you clearly lack sufficient understanding of the topic to have an intelligent discussion about it, therefore, it is in FACT your comments that are invalid and do absolutely nothing to benefit the op in any way, whereas I have in fact made several suggestions that are reasonable and useful to the op to obtain better performance.

|

9/7/2018 8:45 PM
Edited Date/Time: 9/7/2018 8:50 PM

ZB93 wrote:

Not sure how this thread got from helping someone out with a backfire issue, to debating weather skill is more important than ...more

" I think you could form a solid argument for the training over the exhaust in many cases. That doesn't change the fact that the exhaust system will add power to the bike over the stock system."

...and that again proves my point. I can guarantee you with absolute certainty that not a single one of these amateurs could beat a top pro on an identical bike. This means that the amateurs are not using all the power the stock bike has. This means that it is far more intelligent to learn how to ride better instead of increasing the power if one had to choose between one or the other. Also, that $1,000.00 at a training camps is a mere pittance compared to the amount of money one will spend on race gas over pump gas over a years worth of racing etc. There is zero substitute for experience and anyone that thinks there is is not a pro level rider and therefore are unqualified to make that claim.

|

9/7/2018 9:03 PM

ZB93 wrote:

Not sure how this thread got from helping someone out with a backfire issue, to debating weather skill is more important than ...more

barnett468 wrote:

" I think you could form a solid argument for the training over the exhaust in many cases. That doesn't change the fact that ...more

I'm gonna wrap it up on this one... barnett468- With all due respect you are still missing my point: I feel the "save your money just twist the throttle more" argument is counter productive in most of these discussions. Lets create a new thread for that argument, and we can have the debate there. It wasn't what we were talking about here, and derailed the thread.

|

9/7/2018 9:12 PM
Edited Date/Time: 9/8/2018 12:09 PM

ZB93 wrote:

I'm gonna wrap it up on this one... barnett468- With all due respect you are still missing my point: I feel the "save your ...more

I'm not sure exactly who you mean by "we", but actually it was part of the discussion which the op himself brought up in a round about way before I did, and he even stated that he might try mixing race gas 50/50 with pump gas instead of using straight race gas and not tell his son, then check his lap times to see if it is really helping or if it is merely a placebo affect, and I for one think that is a great idea if done properly as to have meaningful results, so if you want to blame anyone for the "twist the throttle" derailment as you call it, I guess you should blame the op for bringing it up in the first place even though it is his thread and should be allowed to post anything he wants on it.

|