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stutter on acceleration

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SaveBluth Avatar
SaveBluth Keith Briscoe
Austin, TX, USA   USA
1976 TR6, SU HS6 carbs. Has original points.

I've noticed that after running/driving for about 10-15 minutes (note: problem doesn't occur in early running), definitely experience a hesitation/stutter upon acceleration. There even seems to be a little miss on neutral throttle while cruising. I think I've noticed that I can lessen the issue by giving significantly more throttle on acceleration, but this of course is not always an option (i.e., in any form of traffic).

Would any of you think this might be related to points? I've had a suggestion to go to one of the Hot-Spark ignition systems. Any other thoughts?

Thanks.
Keith

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poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
Why don't you play around with the timing ?
The distributor is adjustable for timing for a reason.
Every engine has it's own sweet spot.



ZS carb repairs
kencorsaw@aol.com

yycdave Avatar
yycdave Dave More
Calgary, AB, Canada   CAN
1976 Triumph TR6 "Miles"
Keith, to Ken's point I had a similar type of issue on my HS6 equipped 6 but more around the 3000 RPM range. Retarding the timing helped greatly (I'm running 12BTDC indicated). Have you also checked all of your high tension leads to make sure that they're in good shape?



Cheers,
Dave

76 CF58310UO

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maddmapper Avatar
maddmapper Ken Prentice
Victoria, BC, Canada   CAN
The 75 TR6 I purchased has a header and hotter cam which produced a nice throaty sound. The one problem the car had was that it "burped" every once and while while driving. There didn't seem to be any consistency as to when it did it and sometimes it would do it more ofter than others. With the car in the driveway, the air filter off and manually accelerating the car, you could reproduce the "burp" - one of the carbs would belch gas out the carb. I figured it had to be a carb problem and everyone told me it was more than likely the carbs - when was the last time you rebuilt them.

Since I've heard too many stories about people messing with the carbs and just screwing them up further, this was a little out of my league as I had just bought the car and decided to take the car to the local British mechanic guy (you know, the one everyone takes their car to) to get some advice. He opened the hood and immediately told me that the vacuum hose where set up wrong (all my emission stuff has been removed). Off I went to recheck the hoses and make sure there were no vacuum leaks. After that the car still had the "burp".

Back to the British mechanic. Left the car with him for a hour. Apparently the PO had put in platinum plugs (I didn't even think to check the plugs) so those were swapped out and the gap set at 0.025. He put in a new rotor and also set the the timing advance 10 degrees at idle.

It was like a new driving a totally different car, no more "burp" and it runs like a top - was the best $100 and odd dollars I ever spent at the mechanics.

britsnspits Avatar
britsnspits Michael Stoliker
Bethlehem, PA, USA   USA
1976 Triumph Spitfire 1500 "The Phoenix"
1978 Triumph Spitfire 1500 "Lucky"
I don't know why people insist on putting the latest sparkplug technology in these cars since all the other technology is so 1950's. Not that platinum plugs are such modern tech, but it's been known since the 70s that these cars run best on good old copper core plugs with the original factory spark plug gap. Yet I still find NGK BPR5ES gapped however they came out of the box on some poor running car. At least they didn't put in Iridium plugs.

What's wrong with Champion N12Y plugs?

tirebiter Jeff Garber
Dighton, MA, USA   USA
Kieth,

A hesitation upon sudden (even light) acceleration can be very uncomfortable to deal with especially in traffic. These cars did not have issues like this until the advent of emissions control which screwed up a lot of folks. Regardless, the stock factory setup - carbs, ignition system emmissions related equipment and all - would not suffer the owner with an engine that hesitated. Nobody would have bought one if they did.

Typical causes of hesitation are a lean condition or improper spark advance at the instant the throttle is opened suddenly. Air/vacuum leaks can cause a lean condition as can a pinhole or rip in the carb diaphragm. Vacuum advance units on the distributor are used for a reason and the vacuum retard unit accomplishes the same goal (advancing the timing upon sudden throttle opening) just does it with a different vacuum signal.

I'd start by checking the ignition timing to make sure it falls within factory specifications. The mechanical timing advance range (and RPMs) and the vacuum timing advance/retard range (and inches of mercury - "Hg - to produce the timing change) are all listed in the Factory Service Manual.

Once you know the timing is where it should be under all conditions of engine load, RPM and throttle opening, then it's time to work on the carbs. You can bypass the steps to check the timing and go straight to checking the carb diaphragms if you'd like. You might get lucky. A lot of people do not consider the timing specifications to be necessarily set in stone and this is where a lot of time is spent unnecessarily, fiddling with the distributor to see what changes occur, to try to get an engine running without hesitation.

Just my $0.02 worth

dicta dick Taylor
Downey, Callifornia, USA   USA
In reply to # 1300747 by SaveBluth 1976 TR6, SU HS6 carbs. Has original points.

I've noticed that after running/driving for about 10-15 minutes (note: problem doesn't occur in early running), definitely experience a hesitation/stutter upon acceleration. There even seems to be a little miss on neutral throttle while cruising. I think I've noticed that I can lessen the issue by giving significantly more throttle on acceleration, but this of course is not always an option (i.e., in any form of traffic).

Would any of you think this might be related to points? I've had a suggestion to go to one of the Hot-Spark ignition systems. Any other thoughts?

Thanks.
Keith

Keith --- Moons ago, when installing an SU and in an effort to clean up some of the piping, I (mistakenly) connected the vacuum port tube to the banjo vent pipe. Hesitation was the result when trying to cruise at a steady speed. When opening the throttle, vacuum would drop and fuel would then flow into the fuel bowl and everything was OK for a while, till the level in the bowl dropped again. I just recalled this in case you have something similar going on.

Dick

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR7 Drophead "The Great Pumpkin"
1980 Triumph TR8 "Wedgie"
In reply to # 1300747 by SaveBluth 1976 TR6, SU HS6 carbs. Has original points.

I've noticed that after running/driving for about 10-15 minutes (note: problem doesn't occur in early running), definitely experience a hesitation/stutter upon acceleration. There even seems to be a little miss on neutral throttle while cruising. I think I've noticed that I can lessen the issue by giving significantly more throttle on acceleration, but this of course is not always an option (i.e., in any form of traffic).

Would any of you think this might be related to points? I've had a suggestion to go to one of the Hot-Spark ignition systems. Any other thoughts?

Thanks.
Keith

Keith;

Before we all start offering all kinds of well intentioned advice, please post a couple of detailed photos of your engine compartment. These cars have had all kinds of wonky things done to them over the years, and sometimes it can be as simple as a misrouted vacuum line. A photo or two would really help, I think.

A close up photo of a couple of your plugs would be helpful too, so we can see what your mixture is doing. What are you setting your initial ignition timing at? Do you set it with the vacuum line to the dizzy connected?

Vance



1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

stage3 Avatar
stage3 Christian P
Saarbrücken, Saarland, Germany   DEU
Keith

I had similar Problems with one of my cars and started digging into carbs, fuel lines, etc. In the end it was a faulty rotor arm.

Christian

cdozois Avatar
cdozois Gold Member Craig Dozois
Pinehurst, NC, USA   USA
Years ago a friend told me that these kinds of issues rarely involve the carbs, yet most folks usually go to the carbs first. This advice has served me well. The last go around I had, I ignored the manual and reset the timing until it sounded better. Works great.

SaveBluth Avatar
SaveBluth Keith Briscoe
Austin, TX, USA   USA
thanks for all the input. Seems to be a certain amount of agreement on looking at timing/ignition - so, I'll do that first. I'm new at this, but I'll get educated and get help. Also, here are a couple pictures.

Keith


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poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
You may have the wrong coil.
We'll see as we delve a little deeper.
I see the 2 conjoined wires going to the positive side of the coil and I see a black wire also connected to the positive side of the coil.
Where is the other end of that black wire connected to ?



ZS carb repairs
kencorsaw@aol.com

SaveBluth Avatar
SaveBluth Keith Briscoe
Austin, TX, USA   USA
ok - here comes my ignorance... follow the black wire counter clockwise from coil down to the silver cylindrical thing below the rubber pipe (from the smog device). Does that help?

poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
Ok, I think I can see it. It's a non issue if it's what I believe it to be...a static suppressor for the AM radio stations.
Back to the coil.
It appears that by having the 2 conjoined wires actually feeding the coil voltage that you'll need a coil for a ballasted ignition system. That would be a coil with 1.5 or 1.6 ohm resistance.
While there are gold colored coils with that resistance, most common is the gold Lucas sports coil with a 3.0 ohm resistance. The Lucas part number would be DLB105.
Do you see "DLB 105" or "12v" on the bottom side or anywhere on that coil ?



ZS carb repairs
kencorsaw@aol.com



Edited 1 time(s). Last edit at 2015-07-15 10:33 AM by poolboy.

SaveBluth Avatar
SaveBluth Keith Briscoe
Austin, TX, USA   USA
I'll need to check for those markings/indications when I get home to the car. For what it's worth radio is completely disconnected at this time.

If I were to replace coil, are you suggesting that I'd want to get that Lucas Sport Ignition Coil (TRF LUDLB110)? Thanks.

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