Acceleration problem

[Beer van Huet]

When I give a full throttle burst, the engine holds in. The engine accelerates fine up tp 3500 rpm with partial throttle and accelerates to full RPM when I play around a little with the gas handle (about halfway). No backfires or any other symptom. I think its lacking sufficient gas or air or proper ignition when opening the throttle fully. Changed the air filter and cleaned the air filter housing and tubes without any improvement. Put additive in fuel tank twice to clean jets, etc but no improvement. Besides, it will accelerate to full speed after a while with partial gas, so I don't think I have a clogged jet. I am thinking about cleaning the petcock from the inside now. Could there be any obvious reason why the engine does not accelerate with a full burst but only with half throttle?

Looking forward to any suggestions

Beer

[3W-lonerider]

if it were me..i'd tear the vacumm side of the petcock apart and see if there ain't a tear in the diaphram. if thats the case. sometimes the bike run fine as long as you don't go full throttle. petcock not supplying enough gas. happened to me a couple of years ago. bike ran great. but going down the interstate. i'd give it throttle to pass someone and the response just was'nt there. bike would just pick up and go slowly and took it's good ole time picking up speed. tore mine apart and the diaphram had 2 slices in it.

[MP]

+1 on the diaphram.  You have less vacuum on hard accell, so if losing some thru a tear, under full throttle might not have enough to open up petcock.

[AussieValk]

I have the exact same problem. Hard throttle it will gag at 3500 to 4000 rpm. Had carbs sync'd six months back and bike was running fantastic, then suddenly on one hot day bike began to play up. Checked all lines, changed all filters, but not the petcock diaphram, so thats what the problem must be for me. Hope you find whats causing your problems...

[Ricky-D]

You didn't say whether or not, you've done any mods to the bike.

[Zorba]

Could be the vent hose under the tank, diaphram leak or dirty jets, from 1/2 throttle on your "main jets" control the bike , did you put and "Air kit and pipes on it?

[Beer van Huet]

The bike is standard as far as carbs, jets and pipes are concerned. I have taken the vacuum actuator apart from my electronic cruise control because I had a stuck vacuum solenoid valve. I had to take the airfilter box off to get to the actuator. I also ran thru all my electric wiring in trying to fix my cruise control. I noticed that I the hoses from the airfilter to the carbs were not completely fitting the first time I reassembled the airbox, so I fixed that the second time. I also *&^% up the first time by switching the low voltage leads to the 1-2 coil. So I think the air- and ignition are OK now. The bike seems to starve with full throttle. Either the vacuum line ends are worn because I have taken them off so many times now or the fuel valve is (suddenly?) the issue. I will check and clean it. I am reluctant to open the carbs for the first time, since that involves synchronization, special tools and a lot of work. Is there any 'easy way' to check/clean the jets without taking the carbs completely apart? Where exactly do the main jets differ in operation ( as far as inputs are concerned) from the stationary/idle ones? This may lead to my problem.

TIA

Beer

[R J]

When was the last time you replaced all your vacuum lines?

They get old and brittle and crack.

I change mine about every 2nd year of riding.

Just replace them all, no need to try and determine which one is leaking vacuum on ya......

[Beer van Huet]

Bike is 8 years old; never replaced any of the vacuum lines. You have a point there.

[John U.]

The main jets are metered by the jet needles which are tapered and extend into the jet. As the throttle is opened the jet needles are withdrawn, allowing more fuel to pass. However, the main jets being much larger than the slow jets rarely get clogged. The slow jets are operating (meaning allowing gas to flow) at all throttle settings and have a fixed rather than variable metering.
Try some Seafoam or Techron 1 can to no more than 1/2 tank if the jest are partially gummed up that will prbably take care of it.

[Ricky-D]

One thing you do not want to do is mess with removing the carburetors.

If the motor ran fine before, look elsewhere for the fix.

Maybe that aftermarket cruise control is the problem. Sound like it is already a problem. Why have it in the first place?

If the hoses haven't been replaced in eight years, then change them.

A course of SeaFoam would be a recommendation also.

Get the problem corrected before going on to other things which can really complicate matters if not repaired first off.

[f6john]

As a last resort have you done anything to affect airflow to the intake box? I had to put a spacer under the front  gas tank mount to correct a problem I was having. Mine would run like a bat out of hades up to 4000 rpm and then nothing. The spacer would be a quick and inexpensive fix if it would work.

[John U.]

It sounds like your bike is leaning out at high rpms. The suggestions to start with the petcock and vacume hoses are right. Vacume leaks can also be caused by the rubber connectors between the chrome intake tubes and the carbs, or the O-rings that seal the intake tubes to the engine. Also check the intake nipple plugs, they can deteteriorate too.