TR6 TR6 bogs down at 25,000 rpm when accellerating

[conehead53]

All of a sudden my 1976 TR6 is bogging down when accelerating. In experimenting, I found that I can alleviate this problem by pulling the choke out about one-third. However, it concerns me to have to do this. While I realize this may be a caused by a variety of things, I'm hoping this may be something simple to fix.

 

[aerog]

I don't know how the Stromberg carbs on the TR6 work - but the manual-choked SU's choke starts richening the mixture around 1/2 throw (choke 1/2 out). Just an off the cuff thought, maybe your mixture is a bit lean - or something is causing it to lean out at mid-high RPM.



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-- Scott
https://www.aerog.com/mgpage

 

[Basil]

Originally posted by conehead53:
All of a sudden my 1976 TR6 is bogging down when accelerating. In experimenting, I found that I can alleviate this problem by pulling the choke out about one-third. However, it concerns me to have to do this. While I realize this may be a caused by a variety of things, I'm hoping this may be something simple to fix.

Going by the subject of your post, I'm surprise your engine hasn't blown to pieces!! LOL! I mean, "25 thousand RPM" is pretty dang high RPM - like maybe five times redline!

Ok, but seriously, I know that was a typo, but I couldn't resist. The first thing I would check is the oil level in your Carb Dashpots. If low, top it up. You can buy special oil just for those dashpots from places places like Terry's or XKs Unlimited, etc., But what I usually use is just a light motor oil (say, 20 weight). What it sounds like is that your engine is leaning out on acceleration. This can happen when the oil in the dashpots is depleted because, then when you accelerate, the piston in the carb lifts up too suddenly and allows more air than necessary into the combustion chamber, thus leaning it out and usually causing a hesitation or "bogging down."

But with the proper oil level in the dashpots, the piston/jet will raise more slowly under load, thus keeping the mixture right. I'm not promising that is for sure your problem, but that's an easy thing to check and fix if need be.

Check that and let us know how it goes.

Basil

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1967 Jaguar E-Type OTS
1E13333, Silver Blue

[This message has been edited by Basil (edited 08-30-2001).]

 

[conehead53]

Basil: Strange thing happened...the problem went away without doing anything. I checked the oil in the carbs and it was okay. Maybe the gas???? I use an lead additive with highest test gasoline available. Not sure if former owner did this. A friend who also has a TR6 told me not to worry.....the problem is sure to come back! Thanks, Ken

 

[Wingtip]

Originally posted by conehead53:
Basil: Strange thing happened...the problem went away without doing anything. I checked the oil in the carbs and it was okay. Maybe the gas???? I use an lead additive with highest test gasoline available. Not sure if former owner did this. A friend who also has a TR6 told me not to worry.....the problem is sure to come back! Thanks, Ken

Is it a car that hadn't been run in awhile? Maybe old/bad gas like you said. Make sue to check your fuel filter. I'd replace it anyway.

George

 

[StagByTriumph]

Basil: Strange thing happened...the problem went away without doing anything. I checked the oil in the carbs and it was okay. Maybe the gas???? I use an lead additive with highest test gasoline available. Not sure if former owner did this. A friend who also has a TR6 told me not to worry.....the problem is sure to come back! Thanks, Ken

So it now revs cleanly to twenty five thousand RPM? Great!!

I want to buy your engine! /bcforum/images/%%GRAEMLIN_URL%%/bow.gif

 

[DougF]

Who's your engine builder?

 

[Bugeye58]

Pratt & Whitney.
Jeff

 

[BOXoROCKS]

my engine bogs down around 10-10:30 pm

 

[RonMacPherson]

Why are you buying the highest test gas? Did you get your cylinder head "shaved" radically? Is your timing advanced over 35 degrees total @ 2500 rpm.

If not you're wasting your money. Also what year is your TR? You may have mentioned it, and I forgot. Reason why, is most 6 motors after 74 do NOT need lead additive. So another way to save money.

If you're gonna add any additive, I recommend a can of seafoam every 3rd or 4th tankful. Especially if you have to buy an ethanol add mix.

 

[DNK]

Basil- enough with the dancing head. It's giving me a headache

 

[SteveT]

If not you're wasting your money. Also what year is your TR? You may have mentioned it, and I forgot. Reason why, is most 6 motors after 74 do NOT need lead additive. So another way to save money.

So, the heads on '74 and later TR6's are hardened? When you say most "6 motors," what are you referring to, I have a '76? Would adding the lead cause some problems in running the car, such as low RPM hesitation?

Thanks -- Steve

 

[RonMacPherson]

The seats in your 6 should be fine. Adding lead is just emptying your pocket book.

Adding premium, does the same thing. Premium gas just burns quicker, letting one advance the timing, usually gaining a little more power. Unless you have a dyno to set it up on, or are advancing your valve timing also, you should be using regular. Easier to start and why WASTE money?

 

[Adrio]

I had the same thing on my TR4A and it was because the engine was running cold due to a poorly installed thermostat (it was always open). I wonder if there was some reason the engine was cold and not warming up that day. Look into that, as I had a heck of a time figuring it out since ambient temperature now played a big part in my engine performance (given the low air temperature here in the late fall).

 

[vettedog72]

On the surface it sounds like a fuel pump or float problem. If it is the fuel pump the problem will return. I would carry a spare fuel pump for insurance. If it was a float sticking you may never have the problem again.

 

[swift6]

Premium gas just burns quicker, letting one advance the timing, usually gaining a little more power. Unless you have a dyno to set it up on, or are advancing your valve timing also, you should be using regular. Easier to start and why WASTE money?

I thought that higher octane fuels actually had slower burning flame fronts, which allow a more controlled burn, which in turn allows higher cylinder pressures and prevents pre-ignition from hot spots caused by higher compression etc... Lower octane fuels are more volatile, and actually carry more energy, its just harder to control.

 

[Tosh]

The question in the original post does suggest a lean condition. Here is what I discovered when running in my newly rebuilt motor.
It sputtered fiercely and would not rev cleanly over 25,000 (sic) rpm.
Turns out the flexible link between the carbs was loose and only the nearside throttle was operating above idle.
Underway, the only way to accelerate was to pull out the enrichment (choke) knob.

Keep on.

I believe the swift one is correct regarding the nature of high octane fuels.

 

[Twosheds]

I thought that higher octane fuels actually had slower burning flame fronts, which allow a more controlled burn, which in turn allows higher cylinder pressures and prevents pre-ignition from hot spots caused by higher compression etc... Lower octane fuels are more volatile, and actually carry more energy, its just harder to control.

That's what I thought, too.

 

[RonMacPherson]

Okay, I misspoke. Premium fuel burns more COMPLETELY. The heptane and octane strings prevent more than one flamefront occurrence. So in essence it MAY travel a little slower. The burn rate and flame travel with premium is more complete across the combustion chamber, preventing preignition and helping lessen detonation.

I remember reading a Westlake discourse on this years ago, and can not find it quickly. But it will be in the back of my mind and when I come across this I will post it.