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My test ride wasn't great, can anyone spot the fault?

  • Thread starter Thread starter Wes51st
  • Start date Start date
Is there an inline filter between the tank and carbs??? If yes remove it. Its a restriction to good fuel feed to the carbs and its not needed as there is a filter on the petcock. I have also got bikes and found the tank filter had come off the petcock and was rattling around inside. If that happens its a straight line shot for tank crap to get sent to the carbs...follow me???
 
Yes I do know what you mean. There isn't an inline filter and I've cleaned and rebuilt the petcock, it was fine actually. But I will take a look at the internal filter.

I don't like to ask but, anything else?
 
Is the cam chain tensioner working right?? Could the cam chain jumped a tooth and threw the cam timing off? What bike and year is this gagin???
 
Cleaned all the bullet connectors on the harness??? Checked the ground point from the harness to the frame..usually a ring with a black / white wire thats bolted at the front of the battery box mounting bolts.. Free of rust and the ring is solidly to the wire??? Grounds are a gremlin that can make some pretty interesting symptoms at times.
 
You admitted that you were not 100% sure about the pilots. You could spend all day and then some if that is your problem and not get anywhere if you don't make 100% certain that isn't your problem.
 
chuck hahn said:
Is the cam chain tensioner working right?? Could the cam chain jumped a tooth and threw the cam timing off? What bike and year is this gagin???
Click to expand...

Okay, this is an new one to me, perhaps that has happened. It's a 1979 550e
 
chuck hahn said:
Cleaned all the bullet connectors on the harness??? Checked the ground point from the harness to the frame..usually a ring with a black / white wire thats bolted at the front of the battery box mounting bolts.. Free of rust and the ring is solidly to the wire??? Grounds are a gremlin that can make some pretty interesting symptoms at times.
Click to expand...

Yes all the connectors are good, I checked them when I fitted a new rectifier.

I still wonder if too lean is my problem. Would a 3/4 turn on the fuel screw cause it to become more lean then adjusting the air screws could balance out? I did have the fuel screw set to 1 turn, but kept finding sooty plugs, so backed it off to 3/4 when I next removed them.
 
Plugs are probably sooty from running it on the choke system. On VM carbs the bottom pilot screw effects just the idle circuit. After that it transitions to the needle at about 1/8 throttle or so. You fine tune the fuel to air ratio with the side mixture screws. Turning them in will richen a cylinder and out will lean it. I set the pilots at 7/8 as the factory set them pretty lean to satisfy the EPA back then. This little gadget works great on VMs so you can actually SEE what the burn in a cylinder is doing.

Watch the video......

https://www.youtube.com/watch?v=9mKQvWM0nMg
 
Last edited:
I would be sure the ignition advance governor is free and snaps back when you let go of it. Twist it till the weights are all the way open and let go of it. If it is sticky just sand the crank and the bore with some 1500 paper.
 
Thanks for all your help Chuck, you're a gentleman.

The colourtune tool looks really helpful, I'm going to get one. Also that's very useful advice on how the idle system works, I didn't know it that well.

Can I just check; So the fuel mixture screws only effect idle up to 1/8 throttle turn. But the air screws effect at all positions on the throttle?

I think it's the idle which is out and I'm going to reset that back to 7/8 today and let you know how I get on.
 
I've done as Chuck kindly advised, firstly order colortune, then set my fuel mixture screw to 7/8.

I did manage to get my bike running and idling until I turned it off. Now I'm just making small adjustments to the air screw so that it doesn't burn too rich. I check the vacuum and I didn't hear/see any problems.

However, the bike does rev much higher as I close down the choke- does that suggest anything? I've noticed there's no hose attached at the bottom of the air filter- that can't be right, where should it go?
 
Yes on the pilot screws. when i set up one of my bikes I get the colortune to show me that nice blue color at around 1500 RPMs. Then i run it up to around 4500 which is roughly where then tach would be if your doing 70ish MPH and see what it looks like there.

Youll also notice that as you roll on the throttle from idle..or give it quick blip..the color will go orange for a second. Dont worry about that as its normal.

As for the RPMs going up as you let off the choke..First see that the rear ( engine side ) throttle cable has some slack to it as well as the front on and isnt causing a little bit of a hanging idle. Also twist the grip closed well and see if a little extra pressure on the grip makes the RPMs fall. I once had a damaged throttle tube and it was hanging up inside the switch housing.

At an idle with the choke off can you adjust the big idle knob and the revs go down?? You said the bottom pilot screws are at 7/8 but where are the side screws at??
 
Thanks for your continued help.

I have installed new throttle cables actually, as one was missing when I bought it, so thought it best to replace both. So, I don't think that's causing an issue, but will check.

Yes when I adjust the hand screw for idle (forget the actual name but you know what I mean), the revs to fall or increase depending on which way I turn it.

Air screws are currently at 1.5 turns, but I had sooty plugs so will make an adjustment there. However when I tried at 2, 2.5 the engine dies. Despite the sooty plugs, like before, I feel like it's on the leaner side because I'm still getting a slight rumble like backfire in the exhaust. Might be worth mentioning the bike came with a harris 4-1 exhaust installed (years ago apparently), and the previous owner had an extra piece of foam over the air filter lid.

Do you know anything about the hose for the lower part of the air filter?
 
Its just a drain in case the carbs overflow and fuel gets into it basically..that and condensation. I would out some vacuum line on it nd run it down between the tranny and swingarm. Wonder if the exhaust might be a bit plugged?? Mice get in the can and build a nest...it has been known to happen.

Its hard to guess when youre not right there. All I can do is tell you what ive learned and what i have ran into over the years working on bikes.
 
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