Found a new problem

[65fury]

Well on top of my midrange flat spot i now found that if i hold 8-9krpm for too long my engine sounds like it runs outa gas!:bang head: Today i was doing some testing and remembered since powder coating a bunch of parts i forgot to properly ground my rectifier(so i removed powder coating where rectifier bolts) hoping this would help solve my midrange stumble i go for a test ride and found that even at around 7k if i went WOT it would still hesitate so i decided to run in the 8-10k range and suddenly after about a 1/2 mile of running 9k in 4th it fell on its face and started sputtering and dying... until i was going slow enough to be in 1st gear did it regain proper idle and run fine... it did this 3 times, but only does it if im going over 8 or 9k:ummm: what would cause this??

Jason

 

[4gasem]

Floats may need to be adjusted... It may indeed be running out of gas...

 

[65fury]

Floats may need to be adjusted... It may indeed be running out of gas...

Dang....they are all set at 16mm. Would that also cause a midrange issue?? Having the floats off or to low??

jason

 

[maleko89]

16 mm should be fine. Make sure fuel filter is clean and float bowl vents are not kicked and in the proper mounting place.

 

[65fury]

16 mm should be fine. Make sure fuel filter is clean and float bowl vents are not kicked and in the proper mounting place.

okay so i reset my float levels(partially cause im still experimenting with my midrange issue, and cause i wanted to put 160mains in, which by the way made a much stronger top end) fuel filter is clean as a whistle.

After making adjustments to carbs i went for a ride and then outa no where the bike started running like crap! sputtering missing, wont idle at stop signs and sounds like its running on 2 or 3 cylinders, i pulled my front left plug and it made no difference.. what the heck!!! i cant seem to get this bike to run properly ever!!

Jason

 

[gamorg02]

is the bike really made to cruise at 8 or 9k?

 

[65fury]

is the bike really made to cruise at 8 or 9k?

I really dont know, but basically if i wanted to do 100+mph for anything over a 1/4 to 1/2 mile it would act like it ran outa fuel.... which it has never done that before. When i first bought the bike i ran 125mph down the freeway for atleast a mile and it never had an issue

Jason

 

[Rand-5107]

Did you check your fuel tank for rust? Also is your tank vent line clear?

 

[65fury]

Did you check your fuel tank for rust? Also is your tank vent line clear?

Yup, i checked the tank when i first took the bike apart and its very clean. No clogs in anything either. I may have fixed the high rpm fuel run out issue, but i wont know forsure until my bike starts running on all 4 cyl again. Right now it has a miss and i wasnt able to figure out why before it got dark.

jason

 

[naughtyG]

It does sound like one of your vent pipes is kinked or clogged. Check the tank vent, but also all four fuel bowl vents which run to either side of the airbox.

 

[65fury]

Well after Mark told me to check my fuel filter i checked all my lines, all vent and breather lines are fine. I blew thru all the float vent lines and no restrictions.

My now current issue is the bike started running like crap after about a mile of riding, it just suddenly started running on what feels like 2-3 cylinders and wont idle. I dont get it. After reseting all the floats and changing the 165mains to 160s i resynced the carbs and it was running fine, then went for a test ride and before i could test my high rpm fuel issue it just suddenly started running poorly.

If i pull the front left plug while its running it doesnt make a difference, keeps idleing rough and missing.

Also... what causes backfiring and popping in the exhaust? i always get it when down shifting regardless of speed or rpms??(this happened before it started missing)

Thanks

Jason

 

[naughtyG]

If all vents are definitely clear, maybe the fuel inlet to the front left bowl is clogged, or the needle valve isn't working? When it does it, try opening the offending fuel bowl's drain screw - if no gas comes out you found your problem.

Backfiring and popping could be two things:

- air leaks into the exhaust system (connection from header to cylinder is common)
- coasting enrichment diaphragm(s) is or are shot. They are smaller diaphragms on each carb under round covers with 3 screws. Don't think you can get to them without taking carbs out. Check out my carb cleaning thread for details.

 

[65fury]

Good idea, ill check my float bowls tomarrow and see if they all have fuel when its missing. Since i just pulled the carbs i checked my needle valves and floats and everything is very clean and moves perfectly.

As for cleaning the carbs i already have(i read and followed your post on cleaning them too, excellent info) My coasting enrichners looked good and all was cleaned thoroughly so it shouldnt be that. No exhaust leaks either.... ive noticed tho that if my vboost is open it rarely backfires if at all when downshifting, but if i close my vboost it always backfires when down shifting..... why??

jason

 

[naughtyG]

You're absolutely sure you have no air leaks between the airbox and the carbs, and that all the rubber boots between intake and carbs and around the vboost valves are in good (soft rubber not hard) shape and everything's fitted right and air tight?

 

[65fury]

You're absolutely sure you have no air leaks between the airbox and the carbs, and that all the rubber boots between intake and carbs and around the vboost valves are in good (soft rubber not hard) shape and everything's fitted right and air tight?

Yes sirunk: no leaks, ive used all kinds of sprays to check and all the rubbers are in very good shape for being an 86'. Airbox rubber boots are nice and soft and seal well, same with vboost boots.

Jason

 

[65fury]

Okay soooo i got it running again, something was clogging my master carb idle circuit.

But im still having a 4k-7k flat spot grrrrr:damn angry: my bottom end feels great and top end pulls hard, but the middle is just a soggy mess! I noticed if i do a WOT pull from 4k in 5th with vboost open it barely accelerates or pulls and stumbles all the way to 6k, but if i do a WOT pull with vboost closed it still stumbles but not as bad and reaches 6k just a hair faster and cleans up a bit quicker..... i cant understand how im still chasing this issue...... shimming never seems to make much difference if any and my needles are stock. Choking the motor during its stumble doesnt do anything either, and my plugs look fine, light tan straps and white porcelion center with a hint or tan..... could my igniton becutting out in my midrange??

jason

 

[maleko89]

Jason, ALWAYS test ignition and compression before diving into the carbs.

 

[65fury]

Jason, ALWAYS test ignition and compression before diving into the carbs.

Well i tested what i could, i got 13.6-14 volts at idle and it jumps to almost 16v when revved up, highbeams on and blinker going too. All my spark plugs are getting spark, and all my wires and plugs are new.... since it runs great on my bottom end and top end im not sure how to test the ignition during my midrange stumble... is there a way?? Im probably going to go with COPs so that would take care of any coil issues i might have, but are there any other ignition related areas to look that may cause this midrange flat spot?? Thanks

Jason

 

[maleko89]

Testing if plugs are getting spark is just the first step. You need to check out service manual and test pickup coils, primary and secondary windings of ignition coils, input ignitor voltage, output ignitor voltage (4), plug boot resistance, plug wire resistance. When my dyna coils went bad it would break up in the mid range. Top end and bottom were fine.

 

[jfeagins]

I'd like to point out that "blowing" back through those vent lines doesn't necessarily mean they are unrestricted. Air PRESSURE may be allowed through, but then outside ambient pressure (much lower than your airgun pressure) would still be restricted and not overcome the kink to vent the carb properly.

Maybe try pulling a bit of vacuum on those vent hoses to see just how unrestricted they are......??

Just a thought.........