376 running very lean

[coater87]

 356 cam, 7.25/1 compression, iron head swing arm flash 1958. 376/40 triumph carburetor, 25 pilot, 240 main, 3 and 1/2 slide, 106.5 needle clip in lowest position, 5/16 timing, champion l82c plugs, 11 and 8 for valve clearance.

 Lean, scary lean.

 about 10 years back I had the carburetor sleeved because the slide would stick in the bore near the top.

 Now that its running lean I ordered a 30 pilot, a 107 needle, and a 250 main (i should have ordered more sizes, this stuff coming from across the pond).

 I also order a #3 slide off ebay. Well, the slide came in today, and is so sloppy in the body its un-usable. It appears the guy who sleeved the carburetor just took a skim cut out of the body, then jammed a sleeve over the slide to tighten things up.

 He should have sleeved the body back to round and stock size.

 so I took it for a ride with the loose sleeve anyway, It idles terrible, and still way too lean.

 I am at stock flash jetting (except the needle is 106.5), and way to lean. I have sprayed around the carb and head looking for leaks and cant find any.

 I am running a stock air filter with 2 layers of a cloth like filter and the screens.

 The only things not stock here are the 376/40, and the sleeved body. The electrodes and porcelain are light grey/white after a 10 minute ride.

 I dont want to keep running it like this, it only has 180 miles on the motor.

 any ideas here?

 Lee

[berger]

float height?   maybe,  EDIT hang one your using a slide that's flopping about in the carb? if so it will be lean

[coater87]

Hi  Berger,

 The fuel was right at the pip, but still lean. I made a very thin gasket for under the float needle carrier to raise the level to where it barely does not flood. That did not help.

 Right now it's about 3/32 over the pip.

 Yes, I am stuck with a 3.5 cutaway. If I have to change that it's new carb time. I can't use the 3 cutaway, carb body is screwed up.

 I found a 107 needle jet, gonna try that.


 Lee

[coater87]

 I noticed yesterday the when the back of my hand brushed the carb body it made me pull my hand back. It was very warm.

 I have the tufnol insulator on order, but for now I cut and stacked 5 paper gaskets. The body was much cooler after 40 miles or so.

 I also changed to a 107 needle jet.

 The bike seemed to run better, but it's still lean. I think I spend most of my time between 0 and 1/4 and am just going to have to wait for a 30 pilot jet.

 I dont know much about this carburator, is going from a 25 to a 30 a big jump? The way the spark plugs look, I need a good  amount of change here.

 Lee

[muskrat]

G'day Lee.
Up to 1/4 is pilot and slide. Going up to 30 won't hurt anything once the pilot screw is adjusted. You can make your 3.5 slide into a 3 by taking 1/32" off the bottom. You will need to lift the needle the same amount to compensate.
Cheers

[coater87]

 Ok, 30 pilot 12 mile trip brand new plugs.

 What in the world is going on, I dont think it helped at all.

 Maybe the sleeving killed this carb 

[duTch]

 If it's any consolation, a mate sleeved my slide too, but it's been running fine, except I had to use a .105 needle jet, but otherwise same (25/240 & 3.5 slide).....a couple of weeks ago it started running a bit rough at idle and plugs are now same as yours instead of a bit darker (B6ES)- checked everything except the points so far, maybe this arvo....have you checked yours?

[coater87]

Dutch,

 I have looked at everything I can think of.

 I have always had it in my mind that the color of the electrode was an indication of timing.

 The color of the porceline was an indication of fuel ratio.

 Mine are both white and nothing I do  seems to change this.

 The bike is a one kick starter, it runs well. The motor does not tick (like it's really hot) when you shut it off.

 I am now at 30, 107, 3.5, and 240.

 This same thing happened once way back on a 235 chevy engine. That turned out to be a crack in a manifold that opened up further and further as it got hot.

 I have even checked for a cracked head.

 Maybe I need to change fuel, maybe I am getting garbage readings?? 

 Any other ideas here?

 Lee

 

[groily]

This is all still with the needle in the bottom groove, richest setting,  Lee? And the needle that was in use before I presume??

Given that you're in gentle mode with a new build, you aren't going to be into main jet territory much I wouldn't have thought, and probably much of the time barely on the needle. So upping the pilot ought to have helped a bit at least. If you screw the pilot air adjuster right in, do you get rich black puffs from the exhaust which will blacken the plugs if you leave it ticking over for a few?
I assume the jet block is tightly attached in the body when all is spannered up and that the emulsifier brass titty is in place and shipshape? Not sure quite how important the paper gasket between block and body actually is in practice - but presumably it's 'there for a reason'. And that the top of the carb is a decent fit on a reasonable thread, with the air slide cable's hole blocked if no slide is fitted?

Although the thing has obviously worked in the years since it was sleeved, I wonder do you have another 376 body, even a tired one, which you could swap over using all the same bits, to see if things are different? It might be the only way to establish whether the sleeving has 'done something', or that there is indeed an as-yet undiscovered air leak or crack or something, somewhere.

Given the trouble you take over things, I can't imagine there's anything much up with the ignition side.

I envy all those folk who find carbs to be 'fit 'n forget'. I can't remember doing a carb replacement which hasn't involved some degree of messing around. The instructions supplied by AMAL are perfectly right and proper, but even so, things have a nasty habit of not quite conforming, at least hereabouts. Only one of my machines, fitted with a semi-decent old 376, is rock solid from steady tickover to full bore on 'book' settings - all the others (with newer carbs), be they single or twin set-up, have needed tweaks. Even then, I find that 'perfect can still be the enemy of the good' and that last 1% remains elusive . Better a fraction rich at some points across the range, if there have to be compromises  . . . .

[muskrat]

G'day Lee.
Have you tried spraying WD or carb clean over the carb and manifold while it's running? I've found that some carbs draw in a lot of air around the top cap and cable entry. I smear silastic around them and start it up for 30 seconds then leave overnight to set.
Cheers

[coater87]

 Guys,

 Thanks for the help but I am out of ideas.

 A brand new 376 is a couple hundred bucks.

 To throw the bike on a dyno is 150-200.

 Cheap, cheap, cheap compared to motor damage.

 I think new, unbutchered carb and a jet check on a dyno and things will be good.

 Lee