2006 CRF250R backfire through intake

6/5/2022 6:17pm Edited Date/Time 6/7/2022 6:22am
So I got a 06 crf that had a bad crank bearing. I tore it apart and put in new crank, rod, piston. Checked timing and valves and wouldn’t start. Turns out seats were worn. Got a new reman head from rockymountain. Put in new valves, springs, tappets, etc. Still nothing. Good compression, auto decompression is working. Good spark. Triple checked timing and valve shimming. I’m throwing starting fluid straight into carb and get a back fire flame out of the exhaust and that’s it. Any ideas to try?
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Factor E
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6/6/2022 2:16am
Backfire normally = bad timing
6/6/2022 4:33am
Factor E wrote:
Backfire normally = bad timing
So this thing has a hot cam in it. My timing marks are on but if I’m having a backfire through the carb then the intake valves are staying open too long or not sealing, correct? Maybe move one tooth?
Factor E
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6/6/2022 7:21am Edited Date/Time 6/6/2022 7:22am
post pics of TDC
FGR01
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6/6/2022 7:38am
On the new head, were the seats already cut or matched to the new valves? Did you verify the valve sealing was good after installing the valves?

The Shop

6/6/2022 7:45am
FGR01 wrote:
On the new head, were the seats already cut or matched to the new valves? Did you verify the valve sealing was good after installing the...
On the new head, were the seats already cut or matched to the new valves? Did you verify the valve sealing was good after installing the valves?
Yup that was what I was told was it was ready to accept new valves. They gave me a list and I ordered a new set. Just did a leak down and sounded like a ton of air in the crankcase. Compression test shows 30 psi. I’m gonna try another head gasket and put in new rings.
1
6/6/2022 7:47am
Factor E wrote:
post pics of TDC
Sorry tore it apart already. But the timing dot was on the arrow on the clutch side and my notches on my cam wheel were directly across from each other and in line with the surface of the top of the head.
motoracer58
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6/6/2022 10:15am
cam sprocket could have spun on the cam if the engine locked up which would make your timing marks incorrect
1
6/6/2022 12:11pm
cam sprocket could have spun on the cam if the engine locked up which would make your timing marks incorrect
Crank did seize I am told. Seems pretty unlikely that the cam wheel would spin on the cam unless the bearings froze and then the chain continued to try and drive the cam wheel though correct?
walent215
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6/6/2022 4:07pm
cam sprocket could have spun on the cam if the engine locked up which would make your timing marks incorrect
Crank did seize I am told. Seems pretty unlikely that the cam wheel would spin on the cam unless the bearings froze and then the chain...
Crank did seize I am told. Seems pretty unlikely that the cam wheel would spin on the cam unless the bearings froze and then the chain continued to try and drive the cam wheel though correct?
As motoracer said, its not uncommon to have the gear slip just a tad and be off.
We fought an 09 with a hotcam in it that had that very problem!
I sent the cam in to hotcams and they found that it had slipped.
Sent me a new one free of charge
6/6/2022 4:59pm
cam sprocket could have spun on the cam if the engine locked up which would make your timing marks incorrect
Crank did seize I am told. Seems pretty unlikely that the cam wheel would spin on the cam unless the bearings froze and then the chain...
Crank did seize I am told. Seems pretty unlikely that the cam wheel would spin on the cam unless the bearings froze and then the chain continued to try and drive the cam wheel though correct?
walent215 wrote:
As motoracer said, its not uncommon to have the gear slip just a tad and be off. We fought an 09 with a hotcam in it...
As motoracer said, its not uncommon to have the gear slip just a tad and be off.
We fought an 09 with a hotcam in it that had that very problem!
I sent the cam in to hotcams and they found that it had slipped.
Sent me a new one free of charge
Very interesting! Well if anyone sees this post and happens to have a stock cam to sell I’m interested!
6/6/2022 5:44pm
We’ll just ordered a new Honda oem one. I’m crossing my fingers. I’ll update once installed.
walent215
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6/6/2022 7:14pm
Gotcha
Stage 3 hotcam is available if you’d like to try one
FGR01
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6/6/2022 8:16pm Edited Date/Time 6/6/2022 8:25pm
We’ll just ordered a new Honda oem one. I’m crossing my fingers. I’ll update once installed.
Think I actually have an OEM one. Pretty sure it came out of a 2005.
FGR01
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6/6/2022 8:18pm

Factor E
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6/7/2022 4:41am
Make sure those valves are sealing
6/7/2022 6:22am
Factor E wrote:
Make sure those valves are sealing
10-4. Took it to a mechanic to look over yesterday at lunch. Called this morning and said all good. Gaskets and piston kit should be here late today. New cam late tomorrow.
walent215
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6/8/2022 12:41pm
thats awesome! glad to hear
motoracer58
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6/8/2022 12:45pm
Guess what! Camshaft fixed it. 🤦‍♂️
figured, glad you got it taken care of

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