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Discussion Starter #1
I just finished a new valve job and installing a new carbburetor on my 350. Started right up and idles like a brand new engine but after I start to give it some gas when starting to ride it bogs down and has no power. Took the new carb off and reinstalled the old one. Same thing idles and takes gas fine until you get to a certain RPM or put a load on it.
Anyone have an idea of what's going on. Thanks in advance.
 

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Carburetor adapter boot cracked or torn?

Are you 100% sure valve clearances are correct? Did you roll the engine over by hand and double check your work before closing it up?
 

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Discussion Starter #3
Carburetor adapter boot cracked or torn?

Are you 100% sure valve clearances are correct? Did you roll the engine over by hand and double check your work before closing it up?
Thank you very much for your response. Just took the carburetor boot off and it looks fine. I checked the valve clearance on the table twice and after assembly I checked it twice while turning over the engine 4- 6 times. Everything seemed in perfect order. I don't think the timing is off because it starts and runs great. Should I try some form a gasket on the boot. The seal looks a little flat.
 

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Start it and spray starting fluid (lightly) around the boot to see if the fluid gets into the engine, she'll rev up.
Its acting like low compression, like the valves are not closing fully.
What are your correct valve lash value?
 

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Discussion Starter #5
Start it and spray starting fluid (lightly) around the boot to see if the fluid gets into the engine, she'll rev up.
Its acting like low compression, like the valves are not closing fully.
What are your correct valve lash value?
Thanks a bunch, I'll try the starting fluid. The intake is .006 and the exhaust is .016 which is what I got from the manual.
 

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Those values are critical, I use an angled feeler gauge then check to wiggle by hand, then listen for the tapping sound at idle.
Did you do the straw down the plug hole trick when getting the engine timing determined?
 

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Discussion Starter #7
Thanks for helping Ridgeway! I checked the clearances with a regular feeler gauge (don't have an angled one) and yes compared the feel from each one. I'm not sure what the straw down the plug hole is. I'm 75 years old but that's a new one on me. What is it? May be it's time to learn something new.
 

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A straight feeler blade/gauge can be a problem to get it flat in the gap, any angle can cause a wrong reading. I did this once, thought I was careful but the engine ran like crap after getting everything out back in place. I took a flat blade and bent it myself.
The straw down the plug hole trick is removing the plug to stick a straw, or long pencil down the hole to feel the piston at t.d.c.
The timing marks are one thing, but knowing the piston is up, to then rock the crank back and forth can detect a loose chain and a timing problem causing poor performance.
Here's the problem, or one of the more common....
A guy is turning the crank watching the timing mark come to zero, then oops, just past so the guy turns the crank backwards to make the mark dead on. Did the cam move? or is there slop in the chain. Your'e not suppose to be able to move the crank without the cam moving.
I find the t.d.c., then look at the marks, wiggle the crank to detect a bad chain, then if everything is right, I look at the rocker arm and wiggle the crank again to see what happens. If the lash is reduced the arm moving, if the lash is there the crank will move but not the rocker arm in a very narrow window of the crank rotation.
You could have lash, but at the wrong time, so poor performance feeling the piston can help with the timing. Who needs the stinking timing marks? :)
(don't use a short straw)
 

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Discussion Starter #9
Thanks again Ridgway. I appreciate the education and will make sure to do exactly that in the future. Do you think I could actually be a tooth off in timing? It sure looked good when I was putting it back together. Not sure how it would run if I was. It seems to run so well now without a load on it. I will try the starting fluid and see what happens. If it doesn't have a leak I'll work on the timing. Thanks again.
 

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Did you check or adjust the pilot needles on either carburetor?
 

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Discussion Starter #11
No I did not. I assumed the new carb would have been set. May be I should address that. I have reset the timing but it did not help. Starts right up, sounds good but when you give it gas the RPM's go down and it sounds like it is going to die any second but doesn't, also the plug is jet black. I have 3 timing marks on the flywheel. They are about a quarter of an inch apart and I have been using the center mark to time to. Should I be using one of the other marks?
 

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The engine would most likely not even start if timed incorrectly to the wrong timing marks.

Carburetors are never fully setup from factory. They need some adjustment. Mostly on the pilot needle and idle rpm.
Many aftermarket carburetors come with incorrect jets and require complete rejetting right from new, or never work right at all. Some swap jets from the original carburetor to make them work.
 

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Sounds like valves are too tight...??
Maybe something like that causing the gap in the valves,, definitely sounds like a clearance issues or something with the valves..??
My experiences with aftermarket carbs is they are all junk and should be used as paperweights. I would highly recommend just cleaning and rebuilding your OEM carb,, if that’s an option anyways.
I myself would want to double check my valves and find my way back to my original carb or like others have said like Dezz,, at least use your OEM jets if your gonna use the new carb. Anyways. Ride safe and good luck with it all,, we hope you get it figured out soon!! Please keep us posted on your progress.
 
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