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Vitesse 2ltr Mk I power loss

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jsukey Avatar
jsukey Jason Sukey
Elyria, OH, USA   USA
Could you have a fuel supply issue? The momentary normal acceleration then going off that you can repeat by lifting then getting back on the throttle could be something like a fuel pump not keeping up with high demand, or a restriction slowing down the flow. You may have plenty of flow for idle / free rev in neutral, but not keeping the float bowls filled under power?

Jason

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1492704 by jsukey Could you have a fuel supply issue? The momentary normal acceleration then going off that you can repeat by lifting then getting back on the throttle could be something like a fuel pump not keeping up with high demand, or a restriction slowing down the flow. You may have plenty of flow for idle / free rev in neutral, but not keeping the float bowls filled under power?

Jason

My thoughts exactly! I recently had a pluggeg fuel filter on my pick up truck, it acted the exact same way.

mwatts Martin Watts
Ruinerwold, Drenthe, Netherlands   NLD
This weekend I adjusted the timing using a strobe light and adjusted the carbs a little bit. Issue remains.

I removed the fuel filter, it was very dirty, so I have ordered a new one. Will be here coming week. I was having trouble getting the engine to idle smoothly consistently. It would have momentary drops in revs. Maybe a new fuel filter will fix this issue too.
I suspect the tank could do with a good clean too, so I will be removing that this weekend probably and cleaning it out. Then I only need to hope for some nice weather so I can take it out for a short drive to test.

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Sportsman b pollard
Holyhead, Anglesey, UK   GBR
Hi has the symptoms of electrical malfunction possibly check rotor arm condenser and cap possible tracking
or possibly petrol starvation blocked filter or pump

mwatts Martin Watts
Ruinerwold, Drenthe, Netherlands   NLD
Well, the new fuel filter has arrived and has been installed. I took the tank out and cleaned it. For sure never has been done the past 50 years grinning smiley. The drain plug was stuck so tight it wouldn't come of while the tank was in the car. But I was just about able to remove it with the tank out. There was a little debris in the tank, but not much.

I haven't tested the car with the new filter yet though. Decided now the tank is out it would be a good moment to fabricate a nice little hardboard floor for the boot. It just has carpet in there now. So the tank will go back in when that's done and I'll let you know the results.

Cheers.

TuRtle5 Avatar
TuRtle5 Kevin Kelly
Absecon, NJ, USA   USA
1949 Triumph 2000 Roadster "Coral Mistress"
1959 Triumph TR3A "Drandulet"
1962 Triumph Vitesse "Ohtoseethelightofday"
1968 Triumph TR250    & more
hi Martin, sounds to me like you may be running away from your fuel. if the car can accelerate away from a stop and then suddenly falter it can occur because you used up the fuel in the carburetors and they are not replenished quickly enough to meet demand. If that is the case, problems can be; blocked pick up in the tank, blocked fuel line, (blow air back through line) fuel pump dirty or failing,(disassemble and inspect) cam to fuel pump failing, blocked fuel filter, dirt in carburetors, water in carburetor bowls.

You could be fighting multiple issues, for example a fuel supply problem and a vacuum leak or carburetor mistuned.

especially if you have multiple problems, it is persistence which will win the day!

Best wishes- Kevin

mwatts Martin Watts
Ruinerwold, Drenthe, Netherlands   NLD
Well, I finally had the time to put the tank back in last Friday. And as it was quite nice weather, I decided to take her out for a test drive. Unfortunately, the problem remains.

I checked the fuel flow by disconnecting the fuel line just before the carbs and sticking the fuel line in a transparent bottle. My impression is fuel flow is excellent. I just ran the engine for a few seconds (it ran on the fuel remaining in the carbs) but it was filling up the bottle pretty quickly. My guess is if it would be consuming that much fuel while driving, it would drain the tank in less than ten minutes.

Oh yeah, I swapped the coil with a spare I had laying around too. Didn't make a difference.

So, to recap: engine will run nicely when it is not under load (stationary and free revving), but when accelerating it will suddenly bog down after a few hundred meters, at around 60 km/h. Interestingly, after slowing down momentarily (for instance, taking a roundabout) and accelerating again, the problem will occur earlier (at 30 km/h). So a fuel supply issue is the most obvious, but at first glance it seems to be fine, which is puzzling.

Also, when the problem occurs, the exhaust starts making a deeper sound (as if it's flooding) and there is popping when quickly releasing the throttle. Is that unburnt fuel, and a hint to the problem?

Things I've done: contact breaker gap adjustment, dynamic timing adjustment, new fuel filter, blown air back thru fuel line, cleaned the tank, centered carb needles, fuel mixture adjustment, valve clearance adjustment. After doing all this, I have an engine that starts easily and idles nicely now, but they haven't made any noticeable difference in the "big" issue.

Suggestions I haven't followed up on yet: check for water in carburetor bowls, cam to fuel pump failing (what should I check for?).

So, what to do next?

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Sportsman b pollard
Holyhead, Anglesey, UK   GBR
Sounds like you may want to replace the pump had a similar problem on my GT6

mwatts Martin Watts
Ruinerwold, Drenthe, Netherlands   NLD
I understand what you are saying. The pump is the original one as far as I can tell, and I have no idea if it ever has been serviced in the past 50 years. But judging from the fuel flow I witnessed with the fuel line disconnected, it is still doing quite a reasonable job. How do I judge/measure the performance of the pump, and what should it be? I'dd like to be a little more confident the pump is the issue before taking it apart, spending money on it or running the risk of making things worse..

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Sportsman b pollard
Holyhead, Anglesey, UK   GBR
Difficult to check unless you run the engine on a separate gravity feed you need to check the delivery of fuel per minute
i would fit a new pump assuming you can obtain one on ebay perhaps for a reasonable price ie on uk ebay for £21.00
item 370285917323

Canby, OR, USA   USA
Mine was down on power and struggled to accelerate after easily reaching 30 mph. It turned out to be an issue with the accelerator linkage. I haven't fixed it yet as I'm away from the car for a few months.

Bruce Harding

mwatts Martin Watts
Ruinerwold, Drenthe, Netherlands   NLD
Not working on this issue either at the moment. It's winter, it's cold and wet and the roads are salted. The kind of conditions you better keep British cars inside. winking smiley

ShannonD Shannon Dunn
Raytown, MO, USA   USA
Hi Martin,
The symptoms you site can be caused by a number of things, but I would definitely check timing first. Set the timing to the recommended setting at idle, then slowly advance the throttle and see if the timing advances further and reaches the recommended mark by about 3000rpm. I don't know the specs on your particular engine, but most 4 cylinders will advance about 12-22 degrees from idle timing (which may be 15 dbtdc at idle, meaning the full advance may be 30 degrees or more) at 3000rpm. If it doesn't advance, then you may need to inspect the advance plates in your distributor to see if they are siezed. If you're distributor has a vacuum advance, then check the line feeding it, and also make sure it comes from a port directly behind the carbs right at the inlet manifold. Not all vacuum is the same, and ports not located directly behind a throttle plate (for instance ports further back on the manifold) will not present total vacuum, nor will they present vacuum changes as quickly and responsively as vacuum pulled from right behind the throttle plate. (Check Bernoulli effect, or Bernoulli's equation if you really want to know why there's a difference.)

Also, have you checked compression at the cylinders to be sure they are all presenting correctly? They should all be within about 10% if the motor is in good shape. Anything outside of that spec would suggest there may be other problems going on...possibly rings not sealing, or valves not seating properly, or worn valve guides, all of which can cause changes in the plug presentation like you mentioned in your post on the rear-most cylinder.

Worn valve springs can also cause similar problems to what you describe. As the engine increases in rpm, the valve springs, if they are weak, will not spring back to proper position fast enough, and tend to bounce the valves at higher rpms causing loss of power at acceleration. Pinging is often caused by timing issues, but if it turns out that the timing is correct, and the advance is operating, then the pinging you hear may be a clue as to warn valve springs. That also causes blow-back into the cylinder and can blacken plugs as you describe.

Anyway, those are just some thoughts. Start with timing first, as it is the easiest to check and most likely to cause this. If it is good, and the distributor appears to advance properly, then check compression, and you will have a better idea where to go next. If the compression test shows significant differences in the cylinders, then a simple vacuum test will indicate more specifically what is going on inside the engine. You can determine exactly what the problems are inside the engine with a vacuum guage. You don't have to open up the engine to look. You just watch the needle on the vacuum guage, and its behavior will tell you exactly what is wrong. If you need assistance in performing these tests, I would be happy to send you a pdf guide as to how to perform them.

GulfTR4 Avatar
GulfTR4 Greg T
St Paul, MN, USA   USA
Check the bearing on your distributor. I had similar problems with 2L GT6+ years ago. Shaft wobble changes the timing. I put in Pertronix and solved timing issue.

Greg

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1511320 by GulfTR4 Check the bearing on your distributor. I had similar problems with 2L GT6+ years ago. Shaft wobble changes the timing. I put in Pertronix and solved timing issue.

Greg

Agree!

Thinking of your symptoms last night. I once had a similar problem on a Datsun, it would run fine all day except for one hill on the way home from work where it would miss fire.
It was driving me crazy, as by the time I got home it would run OK.

Turned out it was a failing points condenser.

I have also had worn distributor shafts on Triumphs which will cause irregular timing scatter.

Electronic ignition kits are cheap and reliable. They inherently give more accurate ignition timing than the stock points set up was, even when new.

Unless you really enjoy buggering about with obsolete electromechanical stuff (some people do) I would convert to EI.

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