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Discussion Starter · #1 · (Edited)
Hi, I bought a raptor 350 a few days ago, It bogs down, sputters and backfires through carburator.
It came with a chinese carb, and the bike had that issue so I opted to mount the original carburetor in it.
The following is what I have tried:

1) Completely dissasembled and cleaned the mikuni carb, replaced the needle valve set and float, needle set, adjusted float level to the right height per manual, pulled out and cleaned all the nozzles and jets and put new o-rings, springs and seals.
Current Setup:
Jet Main: 142.5
Air: 70
Jet: 165
Pilot: 22.5
2) Calibrated intake and exhaust valves per manual
3) Took care of leak on the exhaust (Read online that this could cause it, sounded odd but fixed it anyways)
4) Timing chain marks are lined up, when on TDC, crankshaft T lined up with casing mark, and camshaft sprocket line with the head casing mark.
( the camshaft mark is lined up but when the tensioner pushes in always turnes the camshaft sprocket line slightly of center clockwise) I tried moving the sprocket on chain to see if I could get it to line up perfectly but that is the closest position, so it’s like 1/16” off from the casing mark on the head) maybe the chain is stretched?
5) Read about the Parking brake switch and the reverse switch infamous problems.
The previous owner seems to have removed the parking brake, the only connector by the left head light is the one coming from the clutch, there is no open connectors where it should’ve been for the parking brake.
The reverse switch I tried grounding it but it makes no difference, the bike still sputters and backfires through carb.
6) Compression on motor is good and everything looks stock.
7) No vacuum leaks on rubber boot

Getting ready to pull the head out to check the intake valve to make sure it’s sealing properly, but wanted to ask, maybe someone has any other ideas on what to try before I do this.

I have just worked on automotive weber and dellorto carbs so the problem sounded alot like carburetor issues but I can’t find what else could be wrong with it, everything seems good.
Any help is appreciated!

Thank you,
141537
141538


Roman


 

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If it backfires through the carb or blows the carb out of the boot it is a timing or valve issue.
Double check the valves were adjusted on the correct stroke, and that Both valves are seating properly.
 

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I just got the video to work, and don't see a problem.
It's not going to run correctly without an airbox and air filter with stock jetting.
Put those on and it should run fine.
 

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Discussion Starter · #4 ·
Thanks for replying back, I did try with the filter on many times, it does the exact same thing but you just see and hear the puff through the filter. If you drive it, it just bogs down and wont accelerate at all while you have the gas pressed, it just backfires through the carb. I will record another video with the filter on so you can hear it, but yeah, there is no change.
Valves are adjusted on the proper stroke, how well they are sealing that is a different story, compression is good but I could fill the chamber with air through the spark plug hole and rotate the motor so the valves are sealed one at a time and hear if any of them leak??
Or maybe it would be easier just to remove the head and put some gas on the head chamber around the valve and see if the gas sips through.
 

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It sounds like it needs a valve job then, as you seem to have ruled out most everything else.
As it can only backfire through the carbs from incorrect timing and/or valves(intake) that do not completely close.
I don't remember if there is a compression release in that head or not (been several years since working on a 350).
 

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It sounds like it needs a valve job then, as you seem to have ruled out most everything else.
As it can only backfire through the carbs from incorrect timing and/or valves(intake) that do not completely close.
I don't remember if there is a compression release in that head or not (been several years since working on a 350).
 

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Discussion Starter · #7 ·
Thank you, I just ordered the valve kit + the timing chain. I think I might be able to put the timing chain in without pulling the whole motor out, not 100% sure as I have never changed that on a bike, but will definitely try to avoid the agravation.
I should also have some valve grinding compound around as well.


Thanks again!
 

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Discussion Starter · #10 · (Edited)
Hi, I finally had some time to work on the bike, did the valve job (new valves, valve springs and grinded them with compound until sealing perfectly) put a new timing chain and guides at once and dropped a new carburetor (chinese carb) just to see if it would make a difference.
New exhaust gaskets and also put a new spark plug and coil/cable.
So I can rule those ones out.
Of what I can see, I have a good motor, good compression, good timing, no leaks intake or exhaust.
Not sure what to try now, it still sputters and bogs down, puffs through the carb from around 1000 rpm and up.
1) Maybe a bad CDI? Can they cause this?
2) Another thing I’m still at doubt is the parking brake cable bypass? All the forums mention unplugging it and put in some silicone to avoid water into the connector.
My bike doesnt have the connector or wires at all, nowhere to be found on the harness. The only connector from that side is the one for the clutch switch.
Posted another video, right after I put it together, I will put the link in a sec.



Thank you!
 
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