• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Carbs Running Rich

Share this page

Late to discussion, but My Lotus Elite had same problem, turned out the H4s had wrong jet needles, put in correct ones, turned the nuts down 2 1/2 turns as I recall from 20 yrs ago was correct first shot adjustment and all well.
 
Yeah Why, I think you are just about right. No where in this thread are ; 1] the specific needle type presently in the carbs defined. 2] No where can I find the specific needle type that should be in these carbs spelled out. There are at least 50 different 100 needle types that someone could have put in these carbs. Consequently, it seems we are just /bcforum/images/%%GRAEMLIN_URL%%/whistle.gif Dixie until these points are resolved. Others have suggested that the carbs be sent to some one who know what they be doing /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif---Keoke
 
A couple of people have mentioned the wrong needles on their cars, maybe you are whistling in the dark Keoke, but I know the needles I have are QW, I have just gotten a new set of needles (QW again, which is correct for my car) and jets as well as the gaskets etc.

I just didn't mention it because it is my problem and I knew the needles were correct, though possibly worn, so I didn't mention it. There wasn't really anything to resolve there.

I am sure my 30 years of driving and working on british cars equipped with SU carbs will be able to get me through the process without the need for someone who "knows what they are doing"
 
Don't look like it from where I am setting. CouRse everone else be mind readers--Keoke
 
glemon said:
A couple of people have mentioned the wrong needles on their cars, maybe you are whistling in the dark Keoke, but I know the needles I have are QW, I have just gotten a new set of needles (QW again, which is correct for my car) and jets as well as the gaskets etc.
Click to expand...
I agree, the QW needles should be nearly correct, unless they are mismarked.

You do have H4 carbs with 1.5" bores?

Maybe I missed it, but, they must have 0.090" jets exactly. Just so everyone can relax, you DO have unworn 0.090" jets - right? A #43 drill shank (0.089") should just go into the jet, A #42 (0.093") should not go.

The QW needles should measure exactly 0.089" on the largest step.

And when the jets are adjusted to the fully up position they are near flush with the jet bridge.

And the internal jet washers, springs, cups, & cork seals are installed correctly & in good condition.

Sorry to be a PIA, but if these items are working correctly, the only other reason for it to be too rich is the float levels too high or float inlets not sealing as I mentioned previously. Did you skip a step or "assume" anything?
D
 
Dave, thanks, as I think I mentioned before, I determined it was probably time for a rebuild of the carbs or at least the jets, needles and seals, I am in the process of getting it to the point you are talking about, thanks for those measurments, I have new parts but it never hurts to check them, I was comparing them to the old, and the measurments do indicate slight but measurable wear.

Yes they are 1.5 inch H type carbs as orignally fitted, thanks for the helpful advice--which I always appreciate.

When I get the things back on, adjusted and tested I will post the results.
 
Carbs are rebuilt, got rid of my rich problem, had to mess with the seals on the jets a bit before they would seal, the cork ones supplied weren't doing the job so I substituted O rings.

Still got a miss at 2500 and beyond, took a look at the distributor, the springs were all stretched out so wasn;t getting much benefit from the mech. advance, have done a quick fix, now looking for new springs.
 
Okay, if the springs are stretched, you should be getting mechanical advance quicker; i.e.less resistance against the weights. However that will depend on what your initial timing is, as you may already be into the advance curve.

Should be able to find these springs at any Hotrod shop as kits are sold that contain them, to fit Gm, Mallory and other distributors so someone with a distributor machine can dial in the advance curve. Try your local Hotrod shop, Mr. Gasket, Summit, etc.
 
glemon said:
Still got a miss at 2500 and beyond, took a look at the distributor, the springs were all stretched out so wasn;t getting much benefit from the mech. advance, have done a quick fix, now looking for new springs.
Click to expand...
Hi Greg,
The centrifugal advance should have two springs. The primary spring, usually the lightest, is engaged from the start of the cam rotation. It controls the first portion of a two step advance curve. Usually up to 2,500 engine rpm or so.

The secondary spring, usually heavier, is purposely mounted with some slack in it's end loops so that it only starts to engage at higher rpm. The combination of the two springs then controls the secondary advance from maybe 2,500 engine rpm up.

The total centrifugal advance is limited by a mechanical stop on the arm. The arm will be marked with the total centrifugal advance limit. Something like 12 degrees. This number is in distributor degrees & would be 24 engine degrees.

Recap, the light spring has no slack in it's mounting & controls the lower rpm part of the advance curve. The secondary spring which is slack during the first part of the advance, in conjunction with the primary spring, controls the higher rpm part of the advance curve. A mechanical stop controls the maximum centrifugal advance. - Except see below.

Early Healeys, MG's, etc. with the DM2 type distributor, had a very different "toggle" type advance mechanism which is not very precise or repeatable. Still uses the primary - secondary spring mechanism though it has no actual advance stop.

In my opinion, you would be ahead to have this type advance mechanism replaced with the much better later 25D distributor parts. Someplace like "Advanced Distributors" could do this conversion.
D
 
Dave, please excuse this dumb question but does it matter which spring goes where? Are they marked as to primary and secondary mounting points or is it the total effect of the springs together? Mine work fine but I have never switched the placement when fussing with the dizzy.
Thanks, TH
 
Back
Top