• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Stumble in acceleration... easy fix?

Share this page

C

cjsteak

Freshman Member
Offline
I just recently had the pleasurable (sarcastic) experience of flushing my transmission today, cleaning the outside of it (a foot of accumulated rock hard grease that found it's way onto me) and doing several other things that needed to be done.

Something that this car has always had just got worse for some reason.

This car has always had a very slight off idle stumble when going up a hill in low gear just as you're about to let off the clutch and start moving. Once the clutch is out you can go through any gear at any throttle and it won't stumble.

I just recently adjusted the timing, synched the carbs, cleaned and re-gapped the plugs, checked gap on Pertronix module, checked dash pots and made sure that everything electrical was tip top. The plugs came out a perfect medium tan (first time ever) so I didn't dare touch the mixture. I'm pretty sure it's got something to do with the carbs. Which part of the carbs though? I checked both chokes and they were open and the car was warmed up to normal temperature.

I almost forgot to mention... not only did it stumble worse than before it also gave a muffled backfire as well when accelerating in low gear around 1500-2000 rpm.

Thanks!
driving.gif
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by cjsteak:
...checked dash pots...<hr></blockquote>

Assuming this means you checked that there was adequate oil in there... what weight oil are you using?
 
I've just used 30w motor oil and have never really had a problem with it. I re-checked everything I did earlier and tightened up all electrical connections related to the ignition system, re-synched the carbs (back one was running slower than front slightly), and checked the air cleaners. The problem has been reduced considerably and is actually at the least amount of hesitation it's ever been at. It's nice... but while my hands are still filthy i'd really like to finish off this problem once and for all.
hammer.gif


I might need to take into consideration that these carbs are very old though. Eventhough they've been rebuilt and have fresh parts in them I believe these things get to a point where they are so wore out they just won't fine tune anymore.

Eventhough the problem still exists, this is the fastest this car has ever ran and it actually winds out pretty well. I've been getting 26 mpg these past couple of tanks consistently so i'll be happy if i'm still around that.
 
Hello Cjsteak,
When replacing the caps in the dashpot, you should feell appreciable resistance as the small pistons meet the oil. If they are worn and they go in easily then that is possibly the problem.


Alec
thirsty.gif
 
Two ideas come to mind here ...... use ATF in the dash pots. check the advance weights in the dist.Worn out advance weights can cause this type of thing,( just before they leave you at the side of the road 5 miles from the nearest rock.)
MD(mad dog)
 
I was thinking off idle lean mixture. If the carbs are old, they could be leaking vacuum around the throttle shaft. If the idle mixture is a little lean and you crack the throttle a little bit, it could stumble. Something to think about.
savewave.gif
 
Thank you all for the advice... I think I have a problem that might shed some more light on the subject...

My car is hard to start when it's warm... not too hard but it'll take 5 or 6 cranks and chug until you rev it a lil bit. After that it runs normally with it's typical stumble off idle.

I'm going to check the float level... i'm thinking that it might be off and could be flooding the carbs when it's parked or when it's idling causing the stumble.

Maybe that's why if I start a mintute or two after I shut it down it'll fire right up on the first crank.... but if I let it sit for lets say 10-20 minutes while shopping or something it'll be hard to start.

What do you guys think? Float adjustment?

Thanks!
 
I had the same experience as you describe with my 75 TR6. I took it in to a Jaguar dealer and they told me I had sunk floats. I don't know why, but I thought they might be feeding me a line, so I let it go. Besides stumbling and fumbling on a hot engine, the car would overheat. It almost stranded me a couple of times quite far from home......I couldn't get it started after a long run. The engine would crank, but not turn over. Since I only use the car in summertime, and since the engine seemed to bog down and over heat, I changed the thermostat to a summer thermostat, and its been running superbly ever since. If the surrounding temps are hot, and you're having similar experiences...change the t-stat to a summer one.....It only takes 15 mins, and does it EVER make a difference!
 
Hesitating on throttle under load can be caused by carb piston flutter. either mixture weakening due to carb dashpot oil, or more likely the springs inside are a little slack due to age. Air leaks around manifold and gaskets or throttle spindles.

check ignition advance, vacuum and centrifugal and the points condensor (as this has happened to me in the past.)

As far as poor hot starting and bad running on hot days is concerned this is almost certainly due to the waxstat jets and residual engine heat. A well known problem with Triumphs even in English summers! Fit heat shields between the carbs and exhaust manifold, proper aluminium ones and swap out waxstat jets for non waxstat from earlier SU's if you have em. https://www.su-carbs.co.uk/. While youre at it swap the butterfly valve throttle discs inside for solid ones. All that US emmissions gear makes your Triumph run poorly. Another useful tip for poor starting is flooding float chambers, This can be cured by improved needle (ball) valves from MOSS/Triumphtune and/or making sure the whole fuel pipe float chamber tops, valve seat and valves themselves are air tight when off the car and pressurised, youd be suprised that the slightest leak where the float valve fits into its seat in the chamber top, under pressure from the fuel pump can quickly flood chambers and cause all kinds of problems.
Hope this is helpful.
 
CJ, there are lots of good ideas posted above, and by now you've probably gotten the idea that in order to cure something like a stumble, you'll have to ensure that everything is smack on. You give no indication as to whether this stumble feels like fuel or electric; you could be experiencing poor secondary voltage from the coil or wires with high resistance, oily plugs, too wide a gap, lean mixture, incorrect timing, air leak, or many other possibilities. Look at the plugs and see what color they are. Double check the timing and advance. Am assuming the car has a real gearbox, but if not, there could be any number of problems in an autotranny, including vacuum, hydraulic, brake band adjustment, kickdown cable, clutch pack wear, or valve body difficulties, just for starts.
So, do a very thorough tune up and if it doesn't go away, come back to us with some real specific symptoms, like how the stumble feels (mushy or snappy), what rpm, gear, throttle position and throttle movement rate. Good luck.
shocked.gif
 
Paul,

The problem is fuel / carb / vaccum related.

I'm still experimenting with the helpful suggestions above.

Thanks for your input.
 
Paul,

Forgot to mention... Please read my original post. It will give you a clue as to of what's going on.

In addition, i've never heard of a TR6 with an automatic transmission. Sounds like a horrible thing to do to a TR6 or any Triumph for that matter.

Thanks.
 
Back
Top