CR250 Big Bore Kit or just Porting for low end power?

cable
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cable 9/9/2018 7:41pm
9/9/2018 7:41pm
H4L wrote:
Matt - I highly advise people against milling the base .030" as it kills the topend power. At least with a Gnarly it's an easy fix...
Matt - I highly advise people against milling the base .030" as it kills the topend power. At least with a Gnarly it's an easy fix & all you need to do is change the pipe if you don't like the power characteristic.

Have you done this mod ? I rode an 06 model a few yrs. ago with .025" milled off the base. Felt it was one of the worst mods you can do to these bikes. Varner use to do the .030" mod when these bikes 1st came out & has changed it in the last couple of years. He now does .010 milled off the cyl base unless the owner requests more.

Agree about the CR case reed engines responding really well to port work by a reputable engine tuner. It's been the best bang for your buck in my experience in about 4 decades of riding.
slipdog wrote:
Port timing makes all the difference. Just .030" off and yes, you will lose over rev. I have always taken .040" off the early reed valve...
Port timing makes all the difference. Just .030" off and yes, you will lose over rev. I have always taken .040" off the early reed valve motor mods I did and with transfer and exhaust height changes, over rev actually is increased.
same here. Even the 2001 liked a little taken off. If you do take oft 30 or 40 and dont like it you can add a base gasket.
KX500
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KX500 9/10/2018 5:15am
9/10/2018 5:15am
'Here is a race of a guy on an 03 CR250r racing against a KX500. These bikes are very competitive when tuned right. My guess would be the guy on the 500 got tired at the end of the race.'

I can confirm, that in a race to the 1st turn, 250's aren't really all that far behind a KX500. And yes, a 500 will wear you out.

And as a little trivia, Honda is the only major bike maker to never offer a 2 stroke endure model.
barnett468
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barnett468 9/10/2018 8:55am
9/10/2018 8:55am Edited Date/Time 9/10/2018 9:23am
KX500 wrote:
'Here is a race of a guy on an 03 CR250r racing against a KX500. These bikes are very competitive when tuned right. My guess would...
'Here is a race of a guy on an 03 CR250r racing against a KX500. These bikes are very competitive when tuned right. My guess would be the guy on the 500 got tired at the end of the race.'

I can confirm, that in a race to the 1st turn, 250's aren't really all that far behind a KX500. And yes, a 500 will wear you out.

And as a little trivia, Honda is the only major bike maker to never offer a 2 stroke endure model.
"And as a little trivia, Honda is the only major bike maker to never offer a 2 stroke endure model. "

hmmm...that's odd, i guess these are not a hondas then

MT 125

.
MR175

.
MT250


MTX 125


MTX200


MTX50


They also made this although it is not an enduro.

H4L
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H4L 9/10/2018 8:57am
9/10/2018 8:57am Edited Date/Time 9/10/2018 7:20pm
KX500 wrote:
'Here is a race of a guy on an 03 CR250r racing against a KX500. These bikes are very competitive when tuned right. My guess would...
'Here is a race of a guy on an 03 CR250r racing against a KX500. These bikes are very competitive when tuned right. My guess would be the guy on the 500 got tired at the end of the race.'

I can confirm, that in a race to the 1st turn, 250's aren't really all that far behind a KX500. And yes, a 500 will wear you out.

And as a little trivia, Honda is the only major bike maker to never offer a 2 stroke endure model.
I believe Honda had an off-road CR250r in 94 or 95. It was called a CRE model if I recall.

Put in a search & actually found a thread on Vital by a member.

https://www.vitalmx.com/forums/Old-School-Moto,22/mid-90s-Honda-CRE-250…

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barnett468
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barnett468 9/10/2018 9:02am
9/10/2018 9:02am Edited Date/Time 9/10/2018 9:10am
Kristen_Valentino wrote:
Porting will help, any good tuner can get you where you want it to be, you can always start on the cheap side with a different...
Porting will help, any good tuner can get you where you want it to be, you can always start on the cheap side with a different pipe, you can always by a used head and get it cut with a tighter squish and bigger chamber to get rid of having to run good fuel, I just bought a different head for my bike, I increased squish .020" and tried it out, didn't like it was very soft on the bottom, I recut it and took. 020" off, night and day difference in bottom end, you can call any tuner and see what they suggest, good luck
"Porting will help, any good tuner can get you where you want it to be"

It is absolutely impossible to port a 250 to have big bore type power.
Kristen_Valentino 9/10/2018 11:50am
9/10/2018 11:50am
I agree 100%, it is hard to match what a big bore adds.
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H4L
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H4L 9/12/2018 6:05am
9/12/2018 6:05am
cable wrote:
same here. Even the 2001 liked a little taken off. If you do take oft 30 or 40 and dont like it you can add a...
same here. Even the 2001 liked a little taken off. If you do take oft 30 or 40 and dont like it you can add a base gasket.
It can depend on personal preference I guess. After talking to a couple of the top 2t tuners like Chad Watts, Terry Varner & PC (head of the engine dept. in 05) they all seemed to have a general consensus on removing .010" of the cyl. base for mx use. They've put in the R&D & believe they have very good engine specs in comparison to someone who hasn't.

EG is a good example of it as he mills 030" off & it seems to be a 50/50 mix of those who like the mod vs. those who don't. Even though he reshapes the head to compensate for the base mod the engine doesn't run as good.
Paw Paw 271
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Paw Paw 271 9/12/2018 9:36am
9/12/2018 9:36am
Why not look at the other side of the issue and consider the use of a Rekluse clutch. I have found them to solve a lot of riding issues and they make riding trails much easier. It helps the engine get in a bit of a higher rpm range before full engagement and thus will make trail riding much easier and more forgiving of proper gear selection.

Paw Paw
KX500
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KX500 9/16/2018 7:05am
9/16/2018 7:05am
Got the Gnarly pipe installed yesterday. And bike doesn't want to start. It had been a 1-3 kick bike (hot or cold) since putting the Keihin on it. Finally, after about a dozen kicks it starts. First impression of the pipe was an improvement (I think) but bike was running kind of weird, maybe rich with some hesitation - which had not happened since the carb swap. Then there was a short but serious bogging with a knocking sound and no power. This was the kind of knocking that you'd expect to result in engine locking up. Rode it a few more minutes and bogging/knocking didn't repeat. Stopped and engine dies and doesn't want to restart after another 4 or 5 kicks.

I have put about 4 hours on bike since getting it going. The last ride before changing the pipe, it did the bog/knock exactly 1 time. I was probably half way through the 2.5 mile loop and pushing the bike from there would have really sucked. I finished that loop, got back to the truck, and since bike seemed fine, did another loop with no issues. I was concerned, but since it was just 1 time, thought/hoped it was 1 time only.

I doubt the issue is 'spark knock' but running 93 octane & Yamalube at 40:1. Just guessing, but I imagine piston/cylinder/ crank issues - same as every engine at some point. And nobody really expects a cheap project bike to need nothing done to the engine. I'm just glad to have gotten to ride it a couple times before tearing engine apart. I don't ride that much, so it'll be a good fall/winter project.

Oh and to clarify my comment on 2 stoke Honda enduro bikes, I really meant enduro/off-road racing bikes for the U.S. market. The CRE250 was cool but no thanks to Honda. And the MTX series - I can't even tell if they ever made it to the US.
809
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809 9/16/2018 12:52pm
9/16/2018 12:52pm
After many hours and some $ tuning my CR for woods, I finally said forget it and got a YZ. The power of the YZ is hands down better. I wish I had just started with a YZ to begin with.
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barnett468
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barnett468 9/16/2018 7:33pm
9/16/2018 7:33pm
KX500 wrote:
Got the Gnarly pipe installed yesterday. And bike doesn't want to start. It had been a 1-3 kick bike (hot or cold) since putting the Keihin...
Got the Gnarly pipe installed yesterday. And bike doesn't want to start. It had been a 1-3 kick bike (hot or cold) since putting the Keihin on it. Finally, after about a dozen kicks it starts. First impression of the pipe was an improvement (I think) but bike was running kind of weird, maybe rich with some hesitation - which had not happened since the carb swap. Then there was a short but serious bogging with a knocking sound and no power. This was the kind of knocking that you'd expect to result in engine locking up. Rode it a few more minutes and bogging/knocking didn't repeat. Stopped and engine dies and doesn't want to restart after another 4 or 5 kicks.

I have put about 4 hours on bike since getting it going. The last ride before changing the pipe, it did the bog/knock exactly 1 time. I was probably half way through the 2.5 mile loop and pushing the bike from there would have really sucked. I finished that loop, got back to the truck, and since bike seemed fine, did another loop with no issues. I was concerned, but since it was just 1 time, thought/hoped it was 1 time only.

I doubt the issue is 'spark knock' but running 93 octane & Yamalube at 40:1. Just guessing, but I imagine piston/cylinder/ crank issues - same as every engine at some point. And nobody really expects a cheap project bike to need nothing done to the engine. I'm just glad to have gotten to ride it a couple times before tearing engine apart. I don't ride that much, so it'll be a good fall/winter project.

Oh and to clarify my comment on 2 stoke Honda enduro bikes, I really meant enduro/off-road racing bikes for the U.S. market. The CRE250 was cool but no thanks to Honda. And the MTX series - I can't even tell if they ever made it to the US.
since the bog /knock occurred before and after the pipe install and it is intermittent, it may be electrical.
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2Fmx
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2Fmx 9/20/2018 11:31pm
9/20/2018 11:31pm Edited Date/Time 9/20/2018 11:32pm
I've seen good few guys here using VHM golden head. Anyone here knows what exactly is the improvement from the OEM? They say better overal performance, maybe cooling(?) Does it mean it can help smoothing out the power range, also helping the bottom end performance?
KX500
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KX500 9/22/2018 7:56am
9/22/2018 7:56am
' I finally said forget it and got a YZ'

I'll be looking - may be the best solution.

Got the cylinder pulled off yesterday and found the front half of the piston skirt missing - I guess that Will cause some problems and maybe a knocking sound! Fortunately, the crank seems to be in spec (could get my 0.025" feeler gauge in, looks like 0.040" is spec limit).

Unfortunately, a chunk of piston got up the cylinder wall leaving a nice groove. Oh and then I see the little 'bridge' between the exhaust ports has a crack. Apparently that is very common - and some last a while that way & some don't. So I start looking for a cylinder - yes, good luck with that. They are all just like the one I have or really pricey. And only used for '02-'03 models - cylinders after that require quite a bit to work to use on the earlier models. I guess another reason so many guys go the big bore route and/or bike gets parted out.

My enthusiasm for the CR might be wearing a little thin - but I'll be watching for a decent cylinder. So many parts not working for all model years of the last gen CR250 is certainly a bummer - and a reason I'm really questioning if I want to keep this thing very long. Also another advantage to the YZ.

There was a lot of discussion here about the base gasket and milling this or that. This engine had no base gasket, just a bunch of silicone/rtv smeared in place - who knows what thickness. I also came to realize that the little clips that hold the piston pin in the piston are optional as there were none there. Worked, I guess - amusing I suppose.

barnett468
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barnett468 9/22/2018 7:45pm
9/22/2018 7:45pm
you need to check the rod bearing clearance also, not just the thrust/side clearance.

one guy here here has a thread that says the 265 kit works well, so if you need a cylinder anyway, it now may be a decent option, plus the port timing may already be designed for torque instead of high rpm.

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