Tr4aJim Posted July 15, 2020 Report Share Posted July 15, 2020 Folks, I’m experiencing the type of problem on my TR4a (HS6 carbs), that we all love - one that goes away on its own. When starting out on a drive, the car will hesitate when I try and accelerate. Like I’m driving through molasses. No backfires, just bogging down. If I take my foot out of it, the car runs like nothing is wrong. This behavior lasts for about 5 minutes, slowly diminishing as I drive, until it runs and accelerates perfectly. Before I start out, the car fires up on the first try with about an inch of choke, and I let it idle until the temp comes up. Then choke off (it idles at 900rpm) and off I go. While sitting still, the car revs fine. It’s only when I give it throttle under load, that the hesitation occurs. I’ve tried adding choke again, but it doesn’t help the hesitation. It’s very disconcerting trying to pull away from a stop light or in stop-and-go traffic, as the car just doesn’t want to respond. So I have to give small inputs with the accelerator. Then after driving for 5 minutes or so, all’s well. This is the first time driving the car this year, as I had been rebuilding the rear suspension, but I also have installed a new Pertronix ignition module, a new Pertronix coil, new plugs, cap/rotor and replaced the electric fuel pump. I have checked the carb piston oil, and the pistons move freely. My initial thought was a vacuum leak, that goes away as the engine gets hot. However wouldn’t a vacuum leak also cause issues sitting at idle, or revving at idle? Any ideas of what could cause this “self healing” behavior? Thanks Jim Quote Link to post Share on other sites
RobH Posted July 15, 2020 Report Share Posted July 15, 2020 Mine does that if the petrol is old, so perhaps something to do with poor vapourisation until the carbs and manifold get properly warm. As you say, it goes away as the engine warms up. Quote Link to post Share on other sites
ctc77965o Posted July 15, 2020 Report Share Posted July 15, 2020 What happens if you pull the choke out 1 inch during the misfire episodes? sounds like lean mixtue on warmup Quote Link to post Share on other sites
RogerH Posted July 15, 2020 Report Share Posted July 15, 2020 Hi Jim, Are your carb dash pots topped up.? Roger Quote Link to post Share on other sites
ChrisR-4A Posted July 15, 2020 Report Share Posted July 15, 2020 Bad seal on inlet manifold to cyl head causing air leak when cold which seals itself up as inlet manifold expands. I had exact same on 4A a few years ago, it was the gaskets, got new ones and had to retorque the nuts 3 time over 2 weeks until it finally sealed Quote Link to post Share on other sites
Tr4aJim Posted July 15, 2020 Author Report Share Posted July 15, 2020 Thanks for the responses! Rob - interesting thought. Though I add gasoline “conditioner” in the fall, it is the fuel from last season. Ctc - adding choke, or keeping the choke engaged, doesn’t have an effect. Roger - I checked the dash pot oil after I did the plugs/cap Chris - I’ll try spraying some starter fluid around the intake manifold flanges and see if I get an rpm change. I’ll check the torque too. Cheers Jim Quote Link to post Share on other sites
RogerH Posted July 15, 2020 Report Share Posted July 15, 2020 Hi Jim a couple of years ago (2018 or so) I had serious trouble with my NGK spark plugs. From new they would last 500-1000miles. I tried several sets but they all failed at about the same time. I changed to Champion L87 and they last a good 5000 miles. Roger Quote Link to post Share on other sites
Hamish Posted July 15, 2020 Report Share Posted July 15, 2020 50 minutes ago, Tr4aJim said: Thanks for the responses! Rob - interesting thought. Though I add gasoline “conditioner” in the fall, it is the fuel from last season. Cheers Jim Try a tank of your best octane USA fuel you should notice the difference. 6 month old fuel will go off. Even with a conditioner. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 15, 2020 Report Share Posted July 15, 2020 5 hours ago, Tr4aJim said: Folks, I’m experiencing the type of problem on my TR4a (HS6 carbs), that we all love - one that goes away on its own. When starting out on a drive, the car will hesitate when I try and accelerate. Like I’m driving through molasses. No backfires, just bogging down. If I take my foot out of it, the car runs like nothing is wrong. This behavior lasts for about 5 minutes, slowly diminishing as I drive, until it runs and accelerates perfectly. Before I start out, the car fires up on the first try with about an inch of choke, and I let it idle until the temp comes up. Then choke off (it idles at 900rpm) and off I go. While sitting still, the car revs fine. It’s only when I give it throttle under load, that the hesitation occurs. I’ve tried adding choke again, but it doesn’t help the hesitation. It’s very disconcerting trying to pull away from a stop light or in stop-and-go traffic, as the car just doesn’t want to respond. So I have to give small inputs with the accelerator. Then after driving for 5 minutes or so, all’s well. This is the first time driving the car this year, as I had been rebuilding the rear suspension, but I also have installed a new Pertronix ignition module, a new Pertronix coil, new plugs, cap/rotor and replaced the electric fuel pump. I have checked the carb piston oil, and the pistons move freely. My initial thought was a vacuum leak, that goes away as the engine gets hot. However wouldn’t a vacuum leak also cause issues sitting at idle, or revving at idle? Any ideas of what could cause this “self healing” behavior? Thanks Jim My 4 cyl TR does exactly that. Once thoroughly warmed it is crisp and responsive. If I richen both carbs by one flat the problem goes away but once warmed through it 'hunts' Meaning it is too rich. Winter time I use a thicker oil in the dash pots to keep it rich on pick up. I use 75 weight gear oil. For summer running I use proper 20 weight dash pot oil Cheers Peter W Quote Link to post Share on other sites
Bleednipple Posted July 15, 2020 Report Share Posted July 15, 2020 5 hours ago, RobH said: Mine does that if the petrol is old, so perhaps something to do with poor vapourisation until the carbs and manifold get properly warm. As you say, it goes away as the engine warms up. Yes I've definitely read that the issue with stale fuel is cold starting/running in particular. The reduction in the volatiles makes the remaining fuel denser than normal which fools the carbs into metering too rich. Which also triangulates with what Peter just said (I think). Nigel Quote Link to post Share on other sites
Tr4aJim Posted July 15, 2020 Author Report Share Posted July 15, 2020 Ok, I guess I’m buying some gas (uh, petrol)! Roger - I think we’re on the same wavelength. I ditched my NGKs for........wait for it........ Champion L87s! cheers Jim Quote Link to post Share on other sites
Tr4aJim Posted August 4, 2020 Author Report Share Posted August 4, 2020 Folks, Here’s an update to this issue. I drained the tank and put in fresh fuel, but the hesitation issue persisted. Pondering what else could cause this, I decided to check the mechanical advance mechanism in the distributor. My car has a Pertronix distributor, that was installed by the PO. I removed the top internal plate and found that one of the weight mechanisms was broken (with lots of metal “dust” all over the insides). So I guess it’s time for a new distributor. I’ll start a new topic on that. Jim Quote Link to post Share on other sites
Opie Posted August 13, 2022 Report Share Posted August 13, 2022 Peter, Thank you! I had the hesitation issue and was pulling my hair out. I tried your suggestion of 80 wt oil this morning and all my hesitation vanished! My only question now is the day is hot here, above 30 celsius (85 F) and that seems to be different than your suggestion regarding seasons. I'll keep the 80 wt oil in until it no longer works or someone advises me otherwise. Opie Quote Link to post Share on other sites
BlueTR3A-5EKT Posted August 13, 2022 Report Share Posted August 13, 2022 2 hours ago, Opie said: Peter, Thank you! I had the hesitation issue and was pulling my hair out. I tried your suggestion of 80 wt oil this morning and all my hesitation vanished! My only question now is the day is hot here, above 30 celsius (85 F) and that seems to be different than your suggestion regarding seasons. I'll keep the 80 wt oil in until it no longer works or someone advises me otherwise. Opie What happens if you drop the mixture nuts ONE FLAT ONLY. on each carb with the regular 20 weight dash pot damper oil? That’s one flat clockwise when viewed from above on each carb to richen the mixture very slightly. Peter W Quote Link to post Share on other sites
Opie Posted August 19, 2022 Report Share Posted August 19, 2022 Peter, I must admit my error in my explanation above of what I thought was happening. 80 wt oil was NOT solving a problem, it was masking a problem. As it happens, my cylinder #3 ignition wire became faulty (probably because I remove the spark plugs so often to check them) and the TR3A was running on three cylinders which it seemed happy to do unless I accelerated. ha. Using 80wt oil in carburetor dash pot damper and a soft foot on the pedal allowed me to get around. After fixing the ignition problem I am correctly back to 20wt oil. Thanks. Quote Link to post Share on other sites
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