Newbie with carb questions...

[rjfoster03]

Recently purchased a 66' Sprite and have a few questions.

In the process of changing all fluids, tune-up, etc... When I pulled the plugs they are sooty black. I know that the prior owner used the choke more than I would think it should be used when driving. I am assuming that it is running rich due to the coloration of the plugs.

The car does "gurgle" / backfire upon downshifting / slowing down.

I am thinking that the carb needs to be tuned and if like my motorcycles, re-jetting is in order.

Am I correct on this?

If so, I need to know what is the best way to handle the re-jetting. I have done this on a honda motorcycle, but the carb is a little different.

<span style="text-decoration: underline">From what I see on the carb:</span>
InterC
Serial # 009541
DGV 5A
32 36

1. Can anyone tell me about the carb that I have?
2. Is this best to have someone "qualified" to do this if I am mechanically able?
3. Best way to select proper size jets?

Thanks for any help.

 

[tahoe healey]

Welcome, but you may want to ask that question of the Spridget forum on this British Car Forum. Although they are are almost the same, they would have more expert insight.

 

[rjfoster03]

Sounds good- thanks.

 

[vette]

rjfoster, If your not sure if the jets were ever changed or there is the most likelyhood that the jets are original, then leave the jets alone. If they were the right size in the beginning then they are the right size now.
One reason some owners find themselves running with the choke out is because the carbs are adjusted too lean. It will not idle beause it is lean and they find that by pulling the chokes out that it will idle. That is because by pulling the chokes out they are enrichening the mixture. Remember, SU carbs provide choke by enrichening the mixture by pulling the jets open alittle. American carbs of the era provide choke by closing off the air flow alittle with the choke plate thereby enrichening the mix.
A lean mix on the air/fuel ratio also would be reponsible for what you may be experienceing as a gurgle or backfire. (of course alittle gurgling is desirous, why do you think we drive these cars)
If your choke is completely off, (an you should ensure that it is not hanging up at the carb/jet linkage) and you still have sooted and black plugs then the carbs are too rich. I would take them off and give them a good cleaning and put them on and adjust them EXACTLY as the book tells you. To check the mix by reading the plug, YOU MUST HAVE COMPLETELY CLEAN PLUGS EACH TIME. The minuetly small adjustments you will make to change the mix will not be enough to reclean the plug if they are sooted badly. It is not hard to clean the carbs. As a matter of fact it can be completely done on the car. But I suggest that for a beginner that you take the carbs off. Take your time, put them on the bench. Clean the Bench off first and clear away an area to work. Do one carb at a time. Even draw yourseld some sketches of the parts you remove and their relative position. And follow the steps in the book. Put them back on the car and adjust By The Book. No Worries, Right.

 

[TimK]

Backfiring/gurgle on deceleration can be caused by bad seals (gasket) between the manifold and the exhaust pipe. Air sucked into the exhaust allows unburned fuel to "pop" on deceleration. Good seals keep oxygen from entering and prevent noisy combustion in the exhaust.

 

[BUNDYRUM]

Hello rjfoster03, it appears you have a Weber carb on your Sprite not an SU. It was a popular conversion and as such you may have to look at some MG websites to get the information on jets and chokes. It shouldn't be too dificult to work it out, as tahoe healey says try the Sprite/Midget forum.

Best regards,

bundyrum.

 

[Legal Bill]

Rjfoster, Bundyrum is right. You have a Weber conversion. The right chokes and jets are important, but so is the initial set up of the engine. Always start with the distributor. Make sure the distributor shaft is not bent and that the body of the distributor is not worn. If you have a Lucas distributor, make sure the vacuum advance is working properly and that there is no vacuum leak anywhere in the intake or the line to the vacuum advance on the distributor. If you still have points, etc, make sure the points, rotor and condensor are new and that the points are correctly gapped. Next, make sure the engine timing is right and the valve adjustment is correct. Carb tuning is the LAST part of any engine tuning and that is especially true in spridgets. Back when I did this stuff for a living, the most frequent problem we would encounter was the owner who fiddled with the carbs thinking that was the problem. there was almost always other problems that had to be addressed first. If you tune the carb to a poorly tuned engine, it may run better, but it will still not run right.

 

[rjfoster03]

Thanks for the information.

I work at a community college and the automotive department is needing cars to look at brakes and I have an appt set up for them to take a look..... The department chair started his career on British cars and he is excited to have the car being brought in. I have already told him I have several questions for him. I will start with the distributor and continue down the list.

Thanks again.

 

[BUNDYRUM]

Hello rjfoster, I have to agree with what Legal Bill says with one exception. If the distributor still has the original points setup and you can afford it then get an electronic conversion to remove the points altogether. In the long run it will save you a lot of headaches.

best regards,

bundyrum.

 

[rjfoster03]

Bundyrum,

You mentioned something that I was wondering about.

Are you referring to something like the Crane Xr-700 Electronic Ignition or replacing the unit with a Pertronix Flame Thrower Electronic Distributor or similar unit?

Thanks

 

[BUNDYRUM]

Hello rjfoster03, Yes exactly, the most popular seems to be the Pertronix. At least with the people here on the forum.

Best regards,

bundyrum.

 

[Legal Bill]

One point to consider, since you are new to the car, you may want to do a compression test and make sure the engine is fundamentally sound before you start putting money in to bolt-on upgrades. How much oil pressure does it have when hot?