free hit
counters
Carb Re-build - Fuel System/Carbs - The Lotus Forums Jump to content
Sign in to follow this  
cly_mitchell

Carb Re-build

Recommended Posts

I need to go through my carbs as I have a small burble at about 1800 rpm. I have never been into a Dellorto before. (many holley, quadrojet, carter ect.) Are there any pitfalls I should be aware of? I am thinking of up sizing my main jets. I am running a HC engine with carbs and making 10psi of boost. I can also adjust for more boost. My future plans also include a Barret :( inner cooler.

I am just looking for some dos and don'ts.

Jack Daniel helped me write this so go easy on my spelling and Texas drawl. :D

Share this post


Link to post
Share on other sites

Upgrade today to remove Google ads and support TLF.

Be prepared for the cost of the kits! Otherwise if you have done a rebuild before you shouldn't have much problem.

Jeff at JAE has some good info. Good luck.

Jeff

Check out the PWR (barrel) air to water intercooler.

http://www.pwr-performance.com/intercooler.htm

Jeff


www.espritturbo.com

Share this post


Link to post
Share on other sites
I need to go through my carbs as I have a small burble at about 1800 rpm. I have never been into a Dellorto before. (many holley, quadrojet, carter ect.) Are there any pitfalls I should be aware of? I am thinking of up sizing my main jets. I am running a HC engine with carbs and making 10psi of boost. I can also adjust for more boost. My future plans also include a Barret :D inner cooler.

I am just looking for some dos and don'ts.

Ive just redone mine..some pointers:

yes the kits cost a fortune.. but get the correct turbo kits.

It is important to make sure the entire system is air tight or youll loose boost... including the pressure balance pipes.. use new fiber washers and dont overtighten the banjos.

Make sure the carb to plenum gaskets are a good seal and same with the plenum cover. I use hylomar.

Also notice the velocity stacks.. IMO they seem too long only leaving about 10mm clearance from the intake opening to the plenum face.. personally I think thats the cause of a lot of the metering problems people are having.. the clearance should be the same as the bore of the stack IMO. I replaced my stacks with 12mm shorties vs the OE 45mm ones.

Make sure all the internal ball check valves are free and sealing properly.

Make sure you adjust the pump pushrods so that they activate the pumps evenly and at the slightest throttle movement.

Make sure the butterflies are adjusted to open together. Set the main throttle stop at exactly zero clearance then mount the carbs on the manifold and zero the adjusters of the second carb from that, that way you should be very close to a balanced startup. Once running you can fine tune if needed. I adjust by focusing on the vibrations and sound until both are smooth as possible... I do the same for the idle mixtures. I tend to be able to fine tune the overall idle mixture strength by the smell of the exhaust (not so much on a cammed engine tho')...its a style I have developed.

I replaced the OE soft mounts because I didnt like the way they restricted the intake flow.. Some say they give better low speed atomization and economy.. but I will find out.. I suspect a small increase in idle jet size would cover the mixture requirement of removing them, at the expense of fuel economy, I expect.

Hope this helps.. you can PM me if you more help along the way. J


If you set no goals you shall surely reach them..

Share this post


Link to post
Share on other sites

Clay, as Jan pointed out its important to use the correct Dellorto kits for use with the Turbo engine.

As the float chamber is boost pressurised on the Turbo, the kits include an orange Nitrile top cover gasket to stop float chamber fuel leakage under boost.

These kits are more expensive, but failure to use them will lead to an engine fire.

Another thing is to be extreemely carefull when removing the float pivot pin, as after a while they seem to corrode themselves in place , and forcing them usually results in the whole tower snapping off from the top cover (scrapping it)

The purpose of the rubber O ring washers (soft mounts) between the carbs and the manifold is to allow the carbs to move slightly to damp out engine vibrations to prevent frothing of the fuel in the float chamber (aeration), which causes awful drivability and running problems. Even the race cars I look after in the shop have these, so I wouldnt advise running without them.

I presume the 910 uses the long inlet trumpets to increase the lenth of the inlet tract, to aid low speed torque , throttle response and drivability. I would think subsituting the short ones will ultimately increase top end power a bit though.

Edited by WayneB

SUNP0003-1.jpg

Share this post


Link to post
Share on other sites
Clay, as Jan pointed out its important to use the correct Dellorto kits for use with the Turbo engine.

As the float chamber is boost pressurised on the Turbo, the kits include an orange Nitrile top cover gasket to stop float chamber fuel leakage under boost.

These kits are more expensive, but failure to use them will lead to an engine fire.

Another thing is to be extreemely carefull when removing the float pivot pin, as after a while they seem to corrode themselves in place , and forcing them usually results in the whole tower snapping off from the top cover (scrapping it)

The purpose of the rubber O ring washers (soft mounts) between the carbs and the manifold is to allow the carbs to move slightly to damp out engine vibrations to prevent frothing of the fuel in the float chamber (aeration), which causes awful drivability and running problems. Even the race cars I look after in the shop have these, so I wouldnt advise running without them.

I presume the 910 uses the long inlet trumpets to increase the lenth of the inlet tract, to aid low speed torque , throttle response and drivability. I would think subsituting the short ones will ultimately increase top end power a bit though.

Good points Wayne..The soft mounts also serve to isolate the carbs from heat soak from the manifold. As far as the trumpets go, I tend to agree, however, I just cant seem to accept the 10mm clearance as a good thing. I think the principle is valid, but I bet any gains in response and drivability are lost as a result. If it wasnt for the boost, I bet performance would suffer at the top end as well (probably does to some degree anyways). The injected cars actually have shorties cast into the plenum.. maybe Lotus realized the same thing I have, and changed them out. I will be able to tell once I get the 85 back on the road (which is looking like early May now)

cheers from BC.. sunny and 17 today.. :)

Edited by f1karting

If you set no goals you shall surely reach them..

Share this post


Link to post
Share on other sites

Clay,

I changed out my idle jets, and eliminated much of the 'tip-in' hesitation @ low RPM.

Keep in mind the difference in the 15% ethanol mix in some gasolines. This may slightly lean out the mixture as opposed to 100% gasoline, especially on the carbed engines that are unable to adjust. Has anyone w/ carbed engines noticed a difference in their mixture due to the recent addition of ethanol?

Nice to see you are able to run 10 psi w/ no problems. What is your compression ratio and how much boost are you planning in the future?

Did we discuss the use of an air fuel ratio meter w/ a wideband 02 sensor elsewhere?

It might help you rejet properly as you increase boost.

Cheers, Lee

Edited by Esprit Aviation

Share this post


Link to post
Share on other sites

Thanks guys, lots of good info. I love this site.

Lee,

I have an HC engine. I researched my records and there was an engine swap/rebuild with HC pistons and other HC components. So compression should be 8.0:1. I say I'm running 10psi because my gauge says that and my gauge says I pop off at 12psi. I also have my boost control at the lowest setting. I don't run the car hard often. I know HCs are kind of running on the edge of too high compression and too much boost. WayneB :) has offered to guide me through the inner cooler install he did. I have aquired the same inner cooler he runs. Getting the intake charge temp down seems to a key element in increasing engine life and maybe some power.

My reasoning behind increasing the main jet size, is to prevent a lean condition. Not really to increase boost.

I don't want to race the car in any way. Way too many Mustangs with blowers in my neck of the woods. I would like to be able to cruise at 85mph without worrying about the motor.

I am also considering a distributorless ignition, like your Eletromotive. It looks alot like a grand by the time I get it in. Seems like alot of geedus to light four a banger.

Cheers

Clay

Share this post


Link to post
Share on other sites

Clay,

Before going to the Electromotive you might want to check out the MSD 6214.

Jeff


www.espritturbo.com

Share this post


Link to post
Share on other sites

Clay,

Don't forget an AFR meter to prove your mixture.

Use any crank triggered system to get rid of the distributor. It is one of my favorite mods to date, nothing under the carbs to light off the fuel if you do get a leak. Nearly failsafe, plus much adjustability. I can change all parameters while sitting in either seat!

How much are the Electromotive HPV-1's going for these days?

Cheers, Lee

Share this post


Link to post
Share on other sites
Clay,

Don't forget an AFR meter to prove your mixture.

Use any crank triggered system to get rid of the distributor. It is one of my favorite mods to date, nothing under the carbs to light off the fuel if you do get a leak. Nearly failsafe, plus much adjustability. I can change all parameters while sitting in either seat!

How much are the Electromotive HPV-1's going for these days?

Cheers, Lee

Why not use the distributor as the trigger and move to a remote coil pack? Saves the need for a crank trigger mod.


If you set no goals you shall surely reach them..

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...