• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

TR2/3/3A TR3@70mph engine seemed to "flatten out" or.....

Share this page

K

karls59tr

Obi Wan
Bronze
Country flag
Offline
TR3@70mph engine seemed to "flatten out" or.....

flutter like it wasnt getting enough gas? ....ran good at all other speeds...took it up to 80 mph to see if it would happen again and it did. I've been doing plug cuts to check the new NGK plugs and they have been a nice grey colour(was running rich with the Champions) I've leaned out the carb mix a little to achieve this.I'm running a header,TR4A intake manifold and mild street cam. I'm wondering if for some reason I'm not getting enough fuel at high speed because of the mods?. I have an electric fuel pump set at 2.5 psi and a newer generic inline gas filter(too restrictive???)Also... could this be a Pertronix issue???
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Sounds like a good idea. So when I reach the higher speeds the gauge will show if I'm really getting the required 2.5 psi? I do have an inline adjuster for fuel pressure.
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Right. Tee the gauge in near the front carb, using a long length of hose so you can lead it out from under the hood and prop the gauge under a windshield wiper. Then take it up to speed and check the fuel pressure when the problem happens. Even 1 psi at the carbs seems to be sufficient. Obviously, this is only a temporary setup.

Most likely the problem is something else, so this will just eliminate fuel delivery as a suspect. But sometimes those pressure regulators do have problems at certain flows, so IMO it's worth doing the test.
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Even if the fuel pressure is correct, you may not be getting sufficient fuel flow for higher RPMs. This happened to me on my old TR3 racecar. Kas Kastner told me to measure the fuel flow.

Disconnect the fuel line from the carburetors and stick the end into a quart container. Turn on the fuel pump and time the filling of the container. Then do the math to convert minutes per quart to gallons per hour. For a race engine, Kas said you need at least 35 GPH, if my poor old brain remembers correctly.

I had about 3.5 GPH. The culprit was the pressure regulator. If a regulator is set to regulate at a pressure that is close to the unregulated fuel pump pressure, the pump and regulator will fight each other and flow will be reduced drastically.

I fixed mine by simply removing the regulator and running the pump sans regulator. All good.
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Have you checked that the backside of the gas pedal is not limited in its travel because of the adjustable bolt behind the pedal and that this may be limiting the gas pedal travel "all the way to the floor" ?

If this is OK, check elsewhere at all the linkage joints, etc. so that someting has not slipped which could be limiting the maximum throttle opening.

Is your fuel filter clogged ?
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Are your float chambers holding enough fuel for high speeds?
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Twosheds said:
Even if the fuel pressure is correct, you may not be getting sufficient fuel flow for higher RPMs.
Click to expand...
Just to be clear, this would show up as reduced pressure at those high rpms. John's test is more practical for a race car, but still only tells you if the flow is sufficient (at zero pressure) when doing the test. It won't eliminate, for example, something that intermittantly blocks fuel flow (like a rock that gets sucked up against the fuel tank pickup).
 
Re: TR3@70mph engine seemed to "flatten out" or.....

Twosheds said:
For a race engine, Kas said you need at least 35 GPH, if my poor old brain remembers correctly.
Click to expand...

Well, I have suffered Brain Fade. I found my old calculations and Kastner recommended 15 GPH, not 35 GPH.
 
Re: TR3@70mph engine seemed to "flatten out" or.....

I read somewhere that a TR owner had his gas tank slushed (interior coated with liquid epoxy - oe whatever) and even though he made sure the hole in the bottom of his gas tank was open, there was a flap of flexible interior coating which flapped enough at low speeds to let the gas through that hole, but at higher speeds where there was a higher demand for more gas, the suction from the fuel pump sucked that unwanted flap down over the outlet to block the outlet in the bottom of his tank.

Maybe I heard it from Don Kelly ?
 
Back
Top