Carburation

[90vanman]

Hi all, can anybody diagnose an idling problem for me? I have an 84 200tlr to which I have recently fitted a copy carb.The carb was fitted to cure idling probs, but it has only partially done so. Above idling it runs OK, but often when closing the throttle, the revs don't die down properly. Also, occasionally when left idling the revs increase on their own.It seems to me like an air leak, but after doing all the usual checks/tests, I am ruling that out. The carb has been set up to the best of my ability using the jets out of the original carb, as there were no markings on the jets from the new carb. Any ideas greatly appreciated, Dave PS its not a Reflex.

[bashplate]

hi, is your throttle cable nice and smooth ? could be jamming up.

[keychange]

It's hard to tell with 'copy carbs" I think some are ok and some are rubbish.

Does your plug indicate a lean mix? if yes check the o-ring on the copy is doing its job then look at the slide movement and compare to the original - the new one should be snugger but not tight - also compare slide cut-away to ensure they are the same.

Did you use original needle - if not I would try that as well.

Failing that throw away the copy and fix the original - they are a good carbie.

[90vanman]

It's hard to tell with 'copy carbs" I think some are ok and some are rubbish.

Does your plug indicate a lean mix? if yes check the o-ring on the copy is doing its job then look at the slide movement and compare to the original - the new one should be snugger but not tight - also compare slide cut-away to ensure they are the same.

Did you use original needle - if not I would try that as well.

Failing that throw away the copy and fix the original - they are a good carbie.

Hi, thanks for the answers, to take the points raised one at a time, the plug is sooty with occasional black smoke from the exhaust. The carb was rejetted with the jets from the original carb and the old needle too. The reason for the change was to get rid of the eternal annoyance of petrol peeing out of the overflow( a problem I have never had with a proper carb like an Amal). The first job I did with the original carb, was to level up the two floats and set the fuel level, but it is almost impossible to get the tag to sit squarely on top of the needle, so I still had leaking. The slide is not the problem afaik, as it can be heard hitting the adjuster screw or bottom of the throttle body every time. This is ruining an absolutely blinding bike, so a cure HAS to be found. Where can I get a proper Viton tipped fuel needle? Dave

[bashplate]

sooty plug/black smoke sounds like over rich jetting...or float bowl flooding or level too high.check that floats aren,t leaking or catching on anything which would stop them moving smoothly. just as a matter of interest, did you try the new carb with the jets it came with?

[keychange]

The old keihin carbies are notorious for leaking floats ie: they gradually fill with fuel and don't float - results in overflow .... it was the first thing I had to do when I got my TLR. If you run carbie dry the fuel in the floats gradually evaporates and when you check they seem ok but 10 minutes after turning on fuel they start to sink

Sooty plug indicates fuel rich which of course could be any part of the carbie mixture system however the way you describe the increase in revs and poor low performance sounds like the float level is not correct - level on your TLR should be 24mm - Failing this make sure you have the correct jets - the old jets may have been changed in an effort to fix the poor performance caused by floats Factory settings - main jet is #98 slow jet is #40 with needle on 2nd - air screw opening is 1 7/8 turns.

Finally make sure your air filter is working properly - the holes on the top of the chamber could be blocked or if you are using a non standard seat it may be causing an air lock _ had this once on a farm bike, cost hundreds stuffing around just to realise the seat had been changed and was sealing the intake.

[90vanman]

Hi everybody, took the bike to Poles Wood yesterday after rebuilding the original carb,straightened out the float arms, reworked the tag that sits against the float needle and refitted the original jets in a thoroughly cleaned out body and it works almost perfectly. Still get a bit of soot on the plug tip, but the throttle response is so much better, no coughing or stumble now. I think I'll live with the sooty plug now the response has improved so much, so thank you to everyone who helped me out on the forum, I hope to meet some of you at some time, Dave.

[keychange]

I think I'll live with the sooty plug

Glad to hear you have it fixed - I would play with the mixture screw - quarter turn at a time then test until you get a nice clean burn.

[Rollox]

...I think I'll live with the sooty plug...

After carb checkup I changed the spark plug from stock NGK DR8ES-L to NGK DR7ES or best DPR7EIX-9. The NGK DPR7EIX-9 Iridium spark is a little wonder and makes the engine less sensitively against carb problems and optimises kickstart and deep revs driving.