Can bad reed cause an engine to fall flat and 4 stroke on the top end ? I am experiencing real hard starting and the bike will not run on the top end. I also noticed what sounds like air coming out the back end of the carb when running.

Any input would be appreciated

Thanks
Jack

Yes, it probably could. How about taking the reed block off and checking it? It's not very difficult.

Also when was your last top end change? Hard starting and losss of top speed is signs of a weak top end

I have taken the reeds out. None of the pedals touched the rubber pads. I turned the reed pedals over and it does not seem to make a difference. Still very hard to start and blubbers at the top end.

The top end was redone recently. all new gaskets and crank seals. My foot hurts from kicking it.

It is strange that I can kick and kick then all of the sudden it will start. Can the bad reeds cause it not to hold idle.

Thanks
Jack

What bike is it?
When was the last time the top end was done?
what is the compression?
crank seals are good?
no air leaks, leak down test done?
Jetting is correct?
Air filter is new/clean?


Just some ideas since we don't have enough information to diagnose any problems you might be having. We could chase something like this around all year long over a forum and never get anywhere.


J.

The bike is a 1981 YZ465 Yamaha

The top end was just redone.
All new gaskets installed and torqued to spec
Compression test was 150 psi
Carb gone through all passages cleaned
New air filter
New crank seals both sides
No cracks or leaks on manifold
Exhaust pipe sealed with high temp silicone

Right after re-assembly it started right up 3 rd kick.
Low end and mid range power good. Top end blubbers and 4 strokes.
Rode sunday and it ran good as long a did not go over a little over 1/2 to 3/4 throttle. Shut bike down after riding for an hour to push my granson up a hill. Went to start the bike and it took at least 20 kicks without a pop then it started all of the sudden.

Started in the garage monday and it took again 15 to 20 kicks with an occasional backfire out the exhaust. When it was running that is when I notice that it sounded like it was having air come back through the carb and out the rear. I took the reeds out and noticed that none of the pedals were touching the reed block. I reversed the pedals and re-installed. There was no difference. It took 15 kicks to start and would not clean out on top end. I have reduced the main to a 370 main from a 380 with no change.

The reason I asked is that I have heard that bad reed pedals can cause hard starting and other problems. Is blubbering on the top end one of them?

Thanks for the input.

Thanks
Jack

No, I would not think so. It really sounds to me like you have a jetting problem, fuel delivery problem, or power valve problem. Dunno if that old yz has power valves though.... Timing off after the rebuild?

Bad reeds can cause hard starting, weak reeds can cause loss of top end. I've seen a fiberglass reed with a small crack keep a CR250 from starting, a new set cured that. I've also seen where somewhen went from stock, stiffer, carbon reeds, to a less stiff fiberglass reed to improve low end but lost some top (flat). Like someone else said you should check all the basics again and include the silencer as a check - was it repacked?

If the reeds are bad enough to not touch the reed block don't just turn them around, THROW THEM AWAY! By turning them around you have just preloaded them against the reed block.

That right there is what I would be looking at.