Help! Carburetor on 250 I-6

[1987 GMC Jimmy]

is a 1988 lesabre or a 1990 olds 88 have a three pin level sensor. I have parts from them but i never checked if i had that. 3800

According to the interchange I saw it’s:

BUICK REGAL 1988-1991
CHEVROLET LUMINA 1990
OLDSMOBILE CUTLASS CRUISER 1988
OLDSMOBILE CUTLASS SUPREME 1988-1990
PONTIAC 6000 1990
PONTIAC BONNEVILLE 1988
PONTIAC GRAND PRIX 1988-1990

Not many years or models, which I think the third leg was just a ground, but it’s been a while since I stared at that page in the shop manual. I thought for sure the ‘90 Olds 88 was another one, but I could just be imagining things. If you had anything like that in your stash, I’d be interested!

 

[JohnTaurus]

According to the interchange I saw it’s:

BUICK REGAL 1988-1991
CHEVROLET LUMINA 1990
OLDSMOBILE CUTLASS CRUISER 1988
OLDSMOBILE CUTLASS SUPREME 1988-1990
PONTIAC 6000 1990
PONTIAC BONNEVILLE 1988
PONTIAC GRAND PRIX 1988-1990

Not many years or models, which I think the third leg was just a ground, but it’s been a while since I stared at that page in the shop manual. I thought for sure the ‘90 Olds 88 was another one, but I could just be imagining things. If you had anything like that in your stash, I’d be interested!

There is a eBay seller called Spark Surplus, I believe they're out of Texas. Anyway, I have found dozens of small, obscure parts that are otherwise difficult to source, all for reasonable prices. Mostly everh thing I buy from them is genuine Ford/Motorcraft, or GM/AC Delco brands, but I have seen other brands as well. If you have a part number, I'd hit them up (or I can search for you, If you'd rather not).

 

[SirRobyn0]

Agree 100% with the caveat on MPFI being my experience with GM 60* V6 injectors, they can be flaky once they get to a certain age, and I’ve also heard bad things about the Gen I spider system, but that once they were upgraded to the Gen III, LS-based style, they were perfect.

My Jimmy will set a code for any little discrepancy, which I’ve always appreciated, but the CCC setup in my Caprice will happily ignore some issues in plain sight, AND I don’t have a serial data pin to hook up my laptop. I do have a 35 year old scanner that can give me 75% of that data, though. I know OBD 1 can be fickle like that. The 128 baud rate on the older ECMs is cartoonish looking at what’s out there today, but if you have a good command on how they work, what they’ll do when they’re messed up, and how to analyze the relatively slipshod data, you can be happy with them on a personal level.

I think TBI is pretty simple, definitely beats the spaghetti you saw in the trucks from 81-86, and I don’t mind having to do the extra work having to manually test sensors like you said. It would get old on multiple vehicles like that, not to mention working on hundreds of them, but mine’s been good to me; even when it’s broken, it’ll tell me things to lead me to the problem. You’ll almost certainly never make the power that you can with a carb/HEI setup, and making TBI more powerful comes with a time/money investment, but even in spite of its limitations, you can work around the inherent shortcomings like the heads, the lame cams, and a partially data blind ECM.

I've got an 84, and yes there can be issues with the vacuum lines I don't disagree with that either. Let me tell you a story the spider system. Years ago I worked for a Goodyear, and the store I was at so happened to be right next to "the van yard", this was the metro transit ride share van yard, they had full size Dodge vans, and Chevy Astro's. They were very good about maintenance, and would do whatever was needed to keep them reliable, if a engine or tranny went, no problem they'd fix it. But a problem with the spider system on the 4.3 Astro, that was to much, they'd sell those vans off. No I'm not kidding, that was the line for them.

I agree TBI is simple, the hardest things in my opinion, is for example an intermittent stall, no codes, no vacuum leaks, clean throttle body, new IAC valve, at that point it's most likely the computer, but could be an intermittent fault in another sensor most likely shorting out and taking the system down, not fun to track that sort of stuff down.

 

[1987 GMC Jimmy]

There is a eBay seller called Spark Surplus, I believe they're out of Texas. Anyway, I have found dozens of small, obscure parts that are otherwise difficult to source, all for reasonable prices. Mostly everh thing I buy from them is genuine Ford/Motorcraft, or GM/AC Delco brands, but I have seen other brands as well. If you have a part number, I'd hit them up (or I can search for you, If you'd rather not).

I’ve bought from them before, possibly several times, can’t remember what. Good idea, I’ll have to check.

 

[CorvairGeek]

Jerry has more ongoing/prospective projects than 85% of the people on here. You might be waiting quite a while for him.

Sad but true

I will keep my eye out for the W-body sensor. I've gotten some requests elsewhere I'm trying to fill as well. I can still access 90s vintage stuff here in the desert (sometimes older too) that people haven't seen in years in many areas of the country.

 

[CorvairGeek]

Agree 100% with the caveat on MPFI being my experience with GM 60* V6 injectors, they can be flaky once they get to a certain age, and I’ve also heard bad things about the Gen I spider system, but that once they were upgraded to the Gen III, LS-based style, they were perfect.

You aren't kidding at all there. The same style, first generation Multitec injectors are also used in the Buick 90 degree V6s. Random misfires and ones that short out hot, killing the engine, but 'unshorting' when they cool off are awesome. Since it is multiple port and not sequential, it kills all injector pulses (instead of half) when they short.
I've manged to avoid the spider injectors myself. I've found the design exceptionally disturbing.

 

[gotyourgoat]

Awesome diagram! Saving that image!

Yes I will plug it in to there, I was thinking about doing that, but I'm so afraid of plugging something in wrong. I very much appreciate that!

(

Well, things are already plugged in wrong or not plugged in at all so what's lost in trying?

Also I don't think you answered @HotRodPC question of do you still have the original carb?

The engine power and truck tech guys did a collaboration build on an inline 6. Made good power even before the boost was added.

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[JohnTaurus]

Well, things are already plugged in wrong or not plugged in at all so what's lost in trying?

Also I don't think you answered @HotRodPC question of do you still have the original carb?

The engine power and truck tech guys did a collaboration build on an inline 6. Made good power even before the boost was added.

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You're right, I didnt answer because I simply forgot. No, I do not have the original carburetor or anything from the old system.

I believe that is why he had no paperwork, etc. I bet he walked in, they took the new one out if the box, he dropped the old one in, and away it went, information and all.

 

[Burb restorer]

Not many of us "Old Timers" are left who used to work on carburetors for a living, just like points, condensers and breaker plates with vacuum advance assemblies. But carburetors, ah yes, those were the days. Carburetors will work like they are supposed to IF you keep the fuel and air supply clean. You can't even buy the ORIGINAL GOOD Solder Seal carburetor cleaner (Or paint stripper) due to environmental concerns so you learn to work around that. Just like setting float levels, a thing of the past. I just wanted to say "Thanks" for posting such clear and precise pictures of your carburetor, you wouldn't believe how many people will NOT post enough AND CLEAR pictures of ANYTHING on the internet. Looks like some of your previous posts are spot on with the missing choke rod as I call it. Here in Florida, we certainly used chokes on 4 and 6 cylinders but many 8 cylinder engines could go without them. Fuel injection is the one important asset to make an engine go hundreds of thousands of miles before a rebuild because of one important action, 14.7 to 1 air fuel ratio, called Stoichiometric Ratio. Carburetors will put excess fuel in the cylinders which wash the oil off the cylinder walls called "Cylinder wall washdown" and this is what makes you piston rings wear MUCH faster over time. But, fuel injection monitors and meters this ratio every second and your piston rings will go MANY more miles happily down the road. Where I grew up, timber was cut and loaded on trucks called "Pulp wood trucks" and the drivers would swear by 6 cylinder engines because of the torque. So go find that missing rod, hook it up correctly to the choke coil on the manifold and go from there. Your hi idle issue should go away too when that choke cam starts to move like it's supposed to. I sure wish we had websites like this when I worked on commission as an automotive technician. Isn't technology great!!

 

[JohnTaurus]

@Burb restorer, excellent post! Thank you so much.

Well, I ran it by the shop today, and the throttle was sticking because the return spring was not in the correct position, it was kinda in a bind. He fabricated me a bracket to hold it, and that is fixed.

As far as the rest of the carburetor issues, he thinks there is something going on with the float in the carburetor. He had it apart several times, but it keeps wanting to flood out at idle. He suggested a rebuild kit, because nothing they tried would fix that issue. I am quite sure it's just a ****** carburetor altogether, personally.

The fuel pump leak was fixed easily, so that's a relief. It was leaking oil, not gas, and we think it's because old cuz didn't put any silicone or any sort of adhesive on the gasket. They did, and it is tight as a drum now, no leaks.

So, Friday (payday), I will order a rebuild kit for the carburetor, and let him see what can be done with that.

 

[JohnTaurus]

Here's a pic of the new bracket and the return spring in a position where it won't be getting in a bind and sticking.

I just took the liberty of concentrating down the pic to show the bracket/spring better. The first pic shows the new PCV valve and grommet that FINALLY arrived, lol.

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[Bextreme04]

Your mechanic did all that and still didn't put a rod on that choke linkage?!?!?

That new bracket and spring setup looks pretty good. One step at a time, its getting there! I'm sure the carb rebuild will help it out immensely.

 

[JohnTaurus]

Your mechanic did all that and still didn't put a rod on that choke linkage?!?!?

That new bracket and spring setup looks pretty good. One step at a time, its getting there! I'm sure the carb rebuild will help it out immensely.

Well, he said he could and will, but he didn't seem to think it was causing any of the problems. He said exactly what you guys were saying about the bracket and that spring on the intake manifold that works it. He didn't think it necessary for normal operation in this climate, but said we can try to find the bracket and make it work, if need be. The way the truck started this past February with freezing temperatures, I dont think it's really going to be a problem. I hope to be going EFI as soon as I can gather all the parts.

I showed him the picture of that blue 250 with the Offy intake and TBI, he agreed that it's a good setup, and we should be able to get it done. I found a used/but not installed offy 4bbl on eBay for $250 (hey! $250 for the 250! Sounds great Haha!). I might get that this pay day, because that's about $150 savings compared to ordering it new. He said I'd need an adapter plate to make it work with the 2bbl TBI, but didnt seem to think that would be an issue.

 

[Bextreme04]

Well, he said he could and will, but he didn't seem to think it was causing any of the problems. He said exactly what you guys were saying about the bracket and that spring on the intake manifold that works it. He didn't think it necessary for normal operation in this climate, but said we can try to find the bracket and make it work, if need be. The way the truck started this past February with freezing temperatures, I dont think it's really going to be a problem. I hope to be going EFI as soon as I can gather all the parts.

I showed him the picture of that blue 250 with the Offy intake and TBI, he agreed that it's a good setup, and we should be able to get it done. I found a used/but not installed offy 4bbl on eBay for $250 (hey! $250 for the 250! Sounds great Haha!). I might get that this pay day, because that's about $150 savings compared to ordering it new. He said I'd need an adapter plate to make it work with the 2bbl TBI, but didnt seem to think that would be an issue.

The issue with how it is right now, is that the choke is always on. There is no bracket or other things to get. All you need to do is bend some welding wire on it so that when that spring on the manifold heats up it lifts your choke lever up to open the choke and let it off the high idle cam. The reason it started fine in the winter is because your choke is ALWAYS on right now. The reason you can't kick it down off the high idle cam is because that lever isn't getting lifted to let it happen. You need to either hook it up, or strap it in the OFF position all the way up. That will make it harder to start when cold, but will keep you from driving around with the choke on and on the fast idle cam.

 

[DoubleDingo]

Here's a pic of the new bracket and the return spring in a position where it won't be getting in a bind and sticking.

I just took the liberty of concentrating down the pic to show the bracket/spring better. The first pic shows the new PCV valve and grommet that FINALLY arrived, lol.

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That alone should make a big difference.