Triumphrat

rmak

I finally got the starting issues resolved with my new 78 T140E with the dreaded MKll's. It starts right up first kick, accelerates like nobody's business.

But just holding the trottle open at 2,000-3,000 rpm going down the road it hesitates and surges, almost like a miss and occasionally spits back through the carb. So just cruising is a problem. I can hold the throttle open to those rpm's in neutral and get the same hesitation and surge, sputtering (sorry, I'm at a loss for descriptive words) too.

Just some facts, compression great and consistant, valves adjusted, coil continuity checked, alternator charges, timing set with strobe, New N5's, I cleaned the carb as best I could and blew out the passages. 2 1/2 turns out. I raised the needle one notch because I thought it was lean. Acceleration improved, and sputtering did improve a little.

I reason, and others have said that ignition parts would be a problem across the rpm range or not be affected by engine speed. Since this problem only occurs at a consistant speed, it's gotta be in the carbs. From what I read the needle jet is the mid range fuel/air supplier, so is that where I should be looking at? needle and jet both visually look good and clean. Another area I'm wondering about is the enrichers. I'm not exactly sure why, mainly because I'm not familiar.

Any and all input appreciated. I tried seaches in all words I could think of with no results.

thirdbike

Definitely sounds like carbs. The sputtering is often indicative of running too rich. You leaned off the carbs because something else wasn't right such as dirty carbs or air leaks, worn jets, throttle slide cutout etc.
Assuming you are all stock including exhaust, I would go back to stock needle setting and try again. Check carb gaskets and crossover. Spray a little ether around (not in) the carbs with engine running and see if engine picks up. If still unresolved, it's time tooverhaul carbs.

motobob

Assuming all jets, emulsion tubes, carb passage ways are clean, float levels correct and spark plugs are not fouling, your first step is to determine whether you are too rich or too lean.

Do you get improvement as the bike warms up?... then too lean.

Take off air cleaners. If improved...too rich.

Does it improve when you partially engage the enrichment mixture?.. too lean.

Moving the needle up and down the clip range is probably the best test.

Typically a bike that is too rich at mid-range will sputter or cough once or twice when accellerating from a low rpm at a heavy load when you reach 1/4 to 1/3 throttle and then clear up as you either accellerate past that point or level your speed out.

A bike that is too lean tends to surge if you try to hold it at a constant throttle setting around the problem rpm area.

I don't mess with the Mark IIs much these days, but I seem to recall the rubber seal at the bottom of the enrichment plunger had a tendency to wear and cause a richness problem at low and mid-range throttle openings.

Another common problem on older carbs is the hole in the needle jets tend to wear causing an over rich condition at mid-range.

rmak

Thanks for the input guys. Just an update.
First off, I recently put on 60's looking cans and took off the air filter, so my reasoning was that I can't be lean with all that added breathing. I'm waiting on a set of pods.

So I took off the carbs, re-cleaned everything and sprayed out the passages. Did the starter fluid spray check. Checked the float setting, checked the plunger rubbers, etc.

I raised the needle one final notch and after kicking for a while (residual cleaner, I believe) It started right up and runs like a champ. Still an occasional pop out through the right carb (?), but no hesitation or jerking when I run with a constant throttle. I may play around with a little bigger jets, but all is cool for now.

68TR6R

With the added "breathing" or airflow, it IS leaner, because there is more air entering the carb per intake stroke. Jet it up a little, don't run lean!

rmak

The Mk2's are now jetted 200 mains, 125 needles and 25 pilots. Does anyone have experience with a setup like mine, with pod filters and more open exhaust that can recommend new jet sizes?

SlowPocono

I was waiting for someone to give you a good answer.

My configuration isn't quite like yours but my 1979 T140E has a two into one exhaust that is too loud but

I'm using the standard air box and filters until I can devise a better system.

The needles are 2C3 with the clip in the middle and the slides have a 3 cutaway.

I recently changed the main jets to 220 and the needle jets to 107.

Both carbs were disassembled and cleaned and the enrichers replaced. I should replace the slides because of wear and to try a different cutaway but I'm reluctant to accumulate $500 in parts experiments for a pair of carbs that could be replaced for a lot less. If you know what I mean.

This new jetting has made a huge improvement in engine performance. It seems to be adequate for riding now but it still isn't perfect.

I hope that is some help.

I discovered that I could order parts online directly from Amal for about half the cost of any other source that I checked.

rmak

Thanks much, Slow. I really appreciate the tip about going directly to Amal. I checked two places for larger needle jets and all they carry was the stock. And I know what you mean about big bucks. I think chrome sliders are $70 a piece. Did you change the pilot?

SlowPocono

The pilots are original.

http://www.amalcarb.co.uk/AmalExplod...99&Spares=true

Amal slides are $27.22.

rmak

I'm bummin. I registered with amalcarb.com and I can't get any info from the exploded carb page. It would have been neat to order a bunch of stuff, but technology has screwed me again.