Hi another Newby here, after lurching in the background for years, Iíve finally joined up and now have a question for the members and hopefully solve my problem.
My in Question is about my 1978 T140 (OIF) last of splayed head model. Iíve owned the bike for the past 4-5 years, slowly getting to know the bike and working on fixing and improving as I go. Iíve put about 2-3 kmís per year, mostly country riding on weekends. most riding is in the range of 2500 - 4500 rpm, so I am able to get good rides without to much of a problem.
After idling or running at low rpm (below 2k) the plug on the right cylinder fouls (sooty black), if the revs are above the 2k, no problems. Plugs foul in as little as 50kís (30 miles).
The problem has been occurring since the top end rebuilt 2000km (1200miles), but, I donít think is related, the worn engine most likely was disguising the problem. Engine has had 800km (500 mile) service. Bike runs great if NOT to much slow running or low rpmís, longer run burns away soot.
Was running points after engine rebuilt, changed to Tri-Spark (Planned upgrade) module ignition, installed by experienced shop. Idle before was OK, slight engine rolling, now steady and even.
Was running NGK 8ís, now running 7ís helps with fouling. New coils, leads, caps fitted. I have iridium 6's but thinking these might be a bit to hot.
Carbís have been re-sleeved, approx 3.5km (2500miles). Have looked over previous threads here, checked Bushmanís site. Float level checked and re-checked, last time I lowered it below 80 thou, about 100thou.
Throttle lift is even. Manifold balance tube replaced, air cleaners cleaned. Checked for air leaks (sprayed with Aero-start) while running. Bike is fitted with Dunstall replica mufflers.
Pilot jet has been cleaned and probed with wire. New viton tipped float needle (alloy) New needle jets (106) new needles, have since lowered the needle (raised clip) smoothed throttle action (not as snappy a response) but better ride. Matching cutaways 3.0ís
Left mixture screw 1 Ĺ turns out, right needs to be 2-2Ĺ turns out. Idling about 800-850 rpm. this setting is best for running.
Most of the treads & Bushman information relate to lean mixture problems at low speed, NOT uneven mixtures.
Going to try measuring and setting fuel level, check tappets clearances, wait for further advice.
Any information to help would be appreciated, hope I have provided all relevant information needed to help you help me.
just to restate, bike runs great until fouled plug, bike is first kick starter, always was/is even with points.
i went with a #3 slide on my tr6 when i had it sleeved and it runs rich too. Plugs are black and exhaust is sooty. But it runs well and the plugs don't foul. i haven't found the $60 for a 3 1/2 slide yet but it's on my list
Re: Amal Rich running at low RPM
#255383 05/25/0911:17 am05/25/0911:17 am
I only probed with the wire (broken clucth cable strand, straightened) after I the found that I had a rich mixture problem. I did this just to make sure I had covered all the normal AMAL problems checked.
Ok, then where is the enrichener on an MKI? All I can think of is the extra little hole which is called the pilot air by-pass circuit. So when Dick mentioned an enrichener, then I thought must be MKII, which I confess I know nothing about, and thus assumed an MKII must have an enrichener.
Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: Amal Rich running at low RPM
#255414 05/25/091:47 pm05/25/091:47 pm
There is an MK 1.5 with an enrichener. I've seen pictures but never in the flesh. These had the body and look of the MK 1 but with an enrichener instead of a tickler. What these were used on, I don't know.
The pilot jet is a jet not a hole! It must be cleaned keeping in mind that the size of the hole, either large (enlarged by poking or the like) or small (partially blocked) will effect idle mixture. Treat it like a jet and use a device that will return it to its original size.
Changing the slide clearance during re-sleeving will change manifold vacuum. As the idle circuit gets its energy to work from manifold vacuum, any changes in slide clearances change manifold vacuum and will effect pilot mixture. While it is possible with typical machine shop practice to set-up the slide with less clearance than the factory did, it will change how the pilot system works. Less clearance will make the pilot mixture richer.
The system is balanced with the slide having .0035 to .0045" clearance in the bore. Also changes that decrease the internal slide clearance presents real safety concerns which include DEATH or worse!
It is popular to set, or balance the slides, when the slides are at the top of their travel. This will increase the problems you will have getting the bike to idle properly and directly effect how you will have to adjust the pilot air screws. If you are to come to grip with these carbs get used to balancing the slides at the bottom of their travel.
There is an assumption that the slides move equally as you open the throttle. This is the case with the Trident with its slide lifting gantry, but when you use cables, especially two individual ones as we do here in the US, the slides do not move in coordination with each other. Variances in routing and movement of the handlebars insure unequal movement.
Turn out both throttle slide screws until the slides can hit the bottom of the carburetor body. Before you start be sure there is enough slack in the cables so the slides are free to hit the bottom of the carburetor body.
Adjust the cable adjusters so both cables lift off the bottom of the body at exactly the same time. When you do this, both slides will produce a distinctive "single" click (not click-click as when the cables are not even) when you release the throttle and the slides hit the bottom of the body. If using a manifold vacuum gage to adjust slide balance be sure to balance vacuum at low throttle openings.
Turn the throttle stop screws until they just hit the slides and continue one full turn on each carb. Turn the pilot air screws out 1 1/2 turns.
The bike will idle at about 1,000 rpm with this setting. Make final adjustments to pilot air screws and move the throttle stops 1/8 turns each in-or-out until the bike idles as you like it. If the pilot air screws end up in different positions (1 1/2 on side 2 1/2 other) check to see if you slides are even (different slide heights will provide different manifold vacuum and variances in the mixture from one carb to the other).
There is a list of things from engine timing, to condition of the rings that will effect manifold vacuum. Variances will cause different manifold vacuum and differences in how the pilot circuit works. The balance tube is an attempt to provide a way of balancing manifold vacuum from one manifold to the other, but it is an imperfect device. It can only do so much and will not fully compensate for big differences in slide height.
As a percentage of error, differences in slide height from side to side, are greater at low throttle openings than at wide open throttle. If one slide is .025" higher than the other at idle it has a dramatic effect on how the bike idles and responds at low throttle openings. The effect would hardly be noticed at 3/4 throttle. At full throttle the slides are clear of the venturi and any differences would have no effect at all.
The variances happen because we are using cables and different routing creates different movement and as we move the bars it changes slide height from one side to the other.
Now the slide cutaway does have an effect upon idle. If you have a slide that is too rich you will have to lean out the pilot air screw to get clean running as you turn the throttle. When trying to get the bike to have clean idle, it is important to get the proper slide - there is overlap between the slide and the pilot circuit.
I asked who sleeved the carbs for a reason, there is a quite disreputable bloke in Melbourne who claimed to do that work but actually farmed it out to a pretty indifferent machinist, if a "warranty" carb came back with a butchered pilot bush it would no doubt go out [recycled] to the next customer.
I am wondering if you got your original carb bodies back.