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post #16 of 19 (permalink) Old 05-21-2019, 03:41 PM Thread Starter
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Join Date: Mar 2019
Location: Ohio
Posts: 22
Quote:
Originally Posted by duke416ex View Post
The cams could have different clearances so that is possible. Do you still have the old exhaust? I would try it as well just to see. I had the same thoughts as far as jetting or an air leak in the intake or exhaust track but it seems like you are covering it. This stuff is hard to diagnose without being there with hands on.
I sold the old pipe, but I did throw the exhaust it had on it when I bought it (stock header & HMF slip-on) which does leak at the can inlet. It didn't do the bloompff sound on shut down, maybe because the slip-on has more back pressure? It still had the spitting & backfire on start up once it was warm though. I just don't get it & its starting to get annoying lol. I'm gonna go to o'reillys and see if I can rent a leak down tester, I just don't see it being a problem with a valve or valve seat.

2006 trx450r


- CP 12:5:1

- 06 CRF Cam

- Empire Industries Exhaust

- No lid w/Uni Filter

- Jogaca Suspension triple rate revalves

- BNR rear shock mod w/GT Thunder link
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post #17 of 19 (permalink) Old 05-23-2019, 03:44 PM Thread Starter
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I took a video of the sound it makes when starting once warm, seems to not be backfiring through the exhaust anymore. Still makes the bloompff sound, pop/cough through the carb though. The sound is muffled in the video, much more noticeable in person. https://youtu.be/9YMyc6l_9HM

2006 trx450r


- CP 12:5:1

- 06 CRF Cam

- Empire Industries Exhaust

- No lid w/Uni Filter

- Jogaca Suspension triple rate revalves

- BNR rear shock mod w/GT Thunder link
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post #18 of 19 (permalink) Old 05-24-2019, 05:56 AM
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Location: Victoriaville, Qc
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You can get a compression tester and check what pressure you are cranking at, may just be a decompressor issue, is it adjusted, throw a feeler gauge in the re should be 0,021-0,023

2008 TRX 450ER XC racing
FMSQ # 281

Last edited by gboezio; 05-24-2019 at 05:58 AM.
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post #19 of 19 (permalink) Old 05-24-2019, 11:13 PM Thread Starter
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Quote:
Originally Posted by gboezio View Post
You can get a compression tester and check what pressure you are cranking at, may just be a decompressor issue, is it adjusted, throw a feeler gauge in the re should be 0,021-0,023
I have messed with the decomp during the cam swap. I had it set at 65 psi, but as I've stated before I took it out & rode it, when I shut it off it had a hard time cranking over, that's when I noticed the backfire issues (bike was never fully warmed up till this point). I checked the cranking compression while it was warm & it was well above 65 psi, struggled to turn over otherwise the reading would've been higher. I ended up setting it while the engine was warm to 50 psi. I do have a feeling that it may be a decomp issue just because of what I just told you. I'm probably wrong though haha.

I just wanna rule a couple things out here & confirmation from you guys would help me. If it was an air leak the backfire/carb spitting would be present all the time, right? Not just on startup & wouldn't matter if the engine was hot or cold. Same with if there was an exhaust leak. The issue only occurs once the engine is warm. I've played with the cam timing during me troubleshooting this issue and a tooth off looks completely not right, so I know my timing is good all corresponding marks are DEAD on. The only other thing I can think of is the Mid-Pipe on the Empire is a slip fit, I can feel/see no exhaust leak there but it may be a possibility?

2006 trx450r


- CP 12:5:1

- 06 CRF Cam

- Empire Industries Exhaust

- No lid w/Uni Filter

- Jogaca Suspension triple rate revalves

- BNR rear shock mod w/GT Thunder link

Last edited by JordtrX; 05-24-2019 at 11:22 PM.
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