What could be cause of death rev ?
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Arm chair racerNew to the board
What could be cause of death rev ?
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Arm chair racerThe day begins with 3WW
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Howdy!
We need more info to best help you.
Are you 1,000% positive the test was done accurately?
Did you try to move the ends of the crank up and down during the test or ever to see if it has excessive bearing wear?
Exactly what are the conditions under which it happens?
Does it always happen?
Does it occur while you are riding or only when the slide is full closed like when you stop riding for a minute and just let it idle?
Are you 1,000% sure the slide is going all the way to the stop screw every time?
Are you 1,000% sure the throttle cable always has freeplay with the throttle closed and is not ever binding, getting pinched or sticking etc.?
About how high does it rev when this occurs?
How does it run?
Look at the slide and see if the chrome has worn away exposing the brass. An excessively worn slide can cause an irregular or high idle, but I've never heard of one causing a death rev.
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Did accurate leak down test yes. Also compression tested. It occurs when after riding at top end speed any gear three and above for a period of more than a minute or two. Bike fails to come back down from rpm. Continues to do so after kill switch removed for approximate 30 sec. I believe it is doing so because of a lean issue. Jetted out everything a few days ago and chopped plug and everything looks good nice cardboard brown ring. Bike starts runs and idles great besides this. Inspected carb and cable everything seems to be ok. Carb is 38 mm mikuni vm
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Arm chair racerThe day begins with 3WW
Howdy!
It keeps running with NO ELECTRICITY?Originally Posted by knipfeldustin
If so, do not let it do this EVER.
How much choke does it when you first start it?
What is the outdoor temp where you first start it?
what is the compression?
Have you checked the timing or changed it from stock?
How far out from full in is the fuel mix screw?
what mods are done?
what octane gas are you using?
do you ever hear it "ping" while riding, especially when first accelerating?
what is your spark plug number?
i would spray FLAMMABLE carb cleaner using the long nozzle gently around the intake boot at idle. if the rpm goes up you have a leak.
if you have no air leak try a 1 step colder plug.
i might go up 1 on the main and pilot for now also until we can narrow the source of the prob down.
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PS - On that bike, the timing is only adjustable if it has an aftermarket kit on it, but it's still possible for it to be off, especially if the flywheel pin is sheared etc..
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Yes it kept running after I pulled the killswitch. It has dg head with dg porting, roost factory silencer, expansion pipe is aftermarket not sure who by. Carb is 38mm. I never have to choke it. Outdoor temps here are mid 60-70 f . Compression tested out at 170. Haven't looked at or touched timing. No pinging noises running pump gas anything between 87-93 octane depending on where I buy. Running stock plug b9es or something like that can't remember off the top of my head. I have tried the starting fluid test and no leaks were found. I just recently went from a 380 main down to a 370 main because it seemed fuel heavy in the low gears and this seemed to help the dogginess. I did not build this motor I purchased this way definitely a top end bike pulls hard 3rd-5th
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Air fuel screw is 1.5 turns out. I've printed and read the 20 page tuning manual on these carbs and have checked and measured everything relatable. Checked float levels and made sure everything was in tolerances. I assume with no air leaks it would be a carb issue but I have found nothing considering just getting a Keihin off an 86 or an air striker 36mm or so
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Has a uni two stage filter with an old school roost factory air box
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Arm chair racerThe day begins with 3WW
hello;
a new carb will not help you since your bike runs with no electricity.
i would stick with 93 octane for now.
if yiu are using a cheap chinese 20.00 compression gauge, it can easily be off 20 lbs to either side. this means that you might have 190 compression which means you might need race fuel even though you can not hear it ping. not all detonation is audible.
if the gauge is right it "should" be fine with 93.
did it do this with the 380 main jet?
i might also try the 380 with race gas or half race gas half 93.
i would stiill try a 1 step colder plug. its cheap easy and fast.
still check the timing. if it is adjustable, then retard it a hair.
would t170 rit is
i woy
srb should not help you unless the s
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mixing fuels of different octane doesn't actually "mix" the fuels, they have different individual specific gravities that basically allow them to separate such as water with different levels of salinity will do when mixed. My idea for a new carb was based on that I believe somehow extra air is being allowed into cylinder and causing the cylinder to "starve" itself which causes the engine to run extra revolutions after deenergizing it. I have nothing to prove its the carb just my assumption as it was the only part not included in the leak down test ??? I will look into timing as I haven't yet .......what I don't understand is why it only does this after I get to the top end of the rpm level of the motor, if I stay half throttle it will not do this just when I run it wide open at the top end it just refuses to come back down, sometimes if I let off throttle completely and shift down through gears this will pull it down but not always. I never really ran it wide open with the 380 jet just because I didn't feel it was running correctly. I appreciate your help !
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It definitely sounds like the combustion chamber is getting hot after a long WOT blast...the motor should not run 30 seconds on it's own after the killswitch is pulled...it's indicative of something in the chamber glowing hot causing it to "diesel". No restrictions in the fuel hose supplying the carb? My thinking is that even though it sounds/feels good everywhere else, that during a long top-end charge, it may be starting to lean out a hair causing the combustion temp/EGT's to spike.
Good luck,
Don
In the works- Honda/Suzuki mutt with XR600R motivation
Last trike- ATC200x w/"S" motor swap, fueled by nitromethane/methanol and stupidity. I wouldn't recommend it.
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Arm chair racerNew to the board
I completely agree with you don. I'm am just simply out of ideas as to the cause I put a new fuel line and filter on when the issue started thinking what you were but to no avail. I'm not sure if needle adjustment or replacement could cause / fix the issue as I'm not too familiar with these finicky mikuni carbs. Almost makes me wonder if porting could be too aggressive also? I'm going to try to race this sat at sikeston ...going up two jet sizes ill run it in practice and if it continues may have to ride back up bike and open up top end to see what I have
Power User
Catch me if you can
It sure sounds like you have an air leak, maybe one that exposes itself only when subject to high heat from the top end runs? Aside from that have you checked the flow of fuel from your tank to your carb? Perhaps if it is badly plugged up you could be running out of fuel on a top end run and then the combination of having run it lean (hot) and a very low amount of fuel in the bowl could cause the revs to go up.
Do the RPMs vary up and down at all when it’s screaming?
Power User
Got the holeshot
The oem stator timing on the 81-84 250r is adjusable. Check your fuel tank gas cap vent to see if its working properly.You should beable to blow threw it.
250r rules
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Arm chair racerThe day begins with 3WW
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Howdy!
You’re welcome, you have an interesting prob and I for one am very curious to know what it is.
See post 4 and 9.
Mikunii carbs are one of the least finicky carbs on the planet.
Porting has nothing to do with it, 0 nada, zilch.
I would not do that. If you do not have time to do all the tests I and others have suggested I would do the following as a hopeful temporary fix.
Run a 10 plug. You may have to go back to the 9 but I doubt it.
Go up 1 on main.
Retard timing just a hair.
Do not lower the slide.
If you get your hands on some race gas mix it 50/50 or go straight and go up 1 more on he main.
look for marks in the combustion chamber. small sharp points can heat up enough to ignite the gas.
I can tell you this. It keeps running because there is enough heat in your cylinder to ignite the gas as another mentioned above. This is the reason I suggested the colder plug. This will reduce the temp of the plug by around
From Champion.
"In identical spark plug types, the difference from one full Heat Range to the next is the ability to remove 158 deg f to 212 deg f from the combustion chamber."
http://www.championsparkplugs.com/le...or---do-i-need
Nothing you have said indicates to me exactly why it is running hot.
Please do all the things I and others suggest even if you might think they are unnecessary.
CARB – By all means try one if you want, however, if you read your own info you can see that there is not one single but of info that suggests to me it is the carb, however, certainly try one if you want.
One of the things you can do is to back out the idle screw until the slide closes all the way. Do NOT let the slide go all the way down immediately after going wot, or you might damage the engine. Let it down close to 0 for at least around 3 seconds first. This is only a temporary test.
There are thousands of people that have run and are still running the old school VM style carbs. Virtually every single race and Championship that was won in the 70’s had one. All the of the Team Green riders had them and won many races and Championships with one on their Tecate's..."The fastest production 3 wheeler in the world.".
See a Mikuni VM on Jimmy Whites Honda slaying, multi Championship Winning bike below.
SLIDE – If the chrome is worn off so you can see the brass in some areas this might contribute to the problem, but this typically simply creates an erratic or slightly high idle prob.
MIXING DIFFERENT OCTANES – I know a little about about gasoline but certainly not everything, you may know more than I, however I not only know that there is NO ZDDP in it but can also guarantee you that if for example, you mix 87 with 93 it will increase the combined fuels resistance to detonation. Zillions of people have done this. Many people here have done this as well as mixing pump gas with race gas for years and their engines have suffered no ill effects from doing so.
I know the people at Lucas where I occasionally buy race gas and both they and VP fuel will also tell you the same thing, however, their standard answer is “We suggest you do not do that”. They will never say it does not reduce the combined fuels resistance to detonation. I am aware that different fuels have different specific gravities, but I can assure you that if you mix them together, the “lighter” gas does not sit on top of the “heavier” gas like oil does on still water. I have actually had water in an engine crankcase before and i can assure you that when i drained it, the oil pump had homogenized it quite well.
This being said, I prefer not to mix fuels.
The reason I want you to try it if it’s possible, is because the racing fuel might run a bit cooler. It does not mean that if it helps you need to run it all the time.
OMG…it’s a talking pig!
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