Help! Carburetor on 250 I-6

[WamboJambo]

Also it's a shame you're not closer; I just finished ripping off my stock intake/exhaust/monojet that have given me zero problems and swapped it for a new intake and headers. Would be interesting to see if swapping on a good intake and working stock carburetor would make your carburetor troubles go away.

 

[JohnTaurus]

Well, I'm going big iron in my tow vehicle. We had a late 60's short bed step-side with an inline 6 and three on the tree when I was a kid and it was a gutless pile of junk.

Heres an interesting inline 6 forum I found when looking around the interwebs. https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=cfrm

This book also looked really informative for I-6 performance improvements. https://www.amazon.com/Chevrolet-Inline-Six-Cylinder-Power-Manual/dp/1931128278/ref=dp_ob_title_bk

Thanks for the links! My memories of an Inline 6 1960s stepside truck was 1965 F-100 with the 240 I-6 and a 4 speed granny low. We stacked three cars (admittedly two without drivetrains), chained them down and that truck pulled them 40 miles or so to the scrap yard. I was extremely impressed as I was in my early 20s and hadn't experienced true "work trucks" at work.

My dad had a bought-new 1992 F-150 Custom with the 300 6 and the 5 speed manual. It was very reliable, towed well and I really liked it. It irks me that he traded it in and what they gave him probably didn't even cover the taxes on the new truck. At 130k, it had a lot of life left, he was just ready to be in something that wasn't a single cab, base model truck with 0 options. But, it was around the time I got my license, and it would have been PERFECT for me.

 

[JohnTaurus]

Also it's a shame you're not closer; I just finished ripping off my stock intake/exhaust/monojet that have given me zero problems and swapped it for a new intake and headers. Would be interesting to see if swapping on a good intake and working stock carburetor would make your carburetor troubles go away.

I'm quite sure it would make a profound difference, lol.

My best friend lives up above Seattle, he acquired a 1970 250 6 that ran great when pulled. He said its mine if I want it, but 3,000 miles is a bit much lol. When I do go to visit, I will be taking my SVT Focus, so I won't be tossing engines into it's cargo hold, lol.


Does anyone know if pretty much any 1974 or older (so, non-intigrated heads) 250 intake will fit this engine? Can someone suggest one in particular? Looking up the stamped GM part number proved fruitless.

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[WamboJambo]

Does anyone know if pretty much any 1974 or older (so, non-intigrated heads) 250 intake will fit this engine? Can someone suggest one in particular? Looking up the stamped GM part number proved fruitless.

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I've been doing a lot of research on this lately and the only ones I see commonly made these days are performance-oriented, and the big names are Offenhauser and Clifford. Both of them make single-quad barrel intakes and triple single barrel intakes, but I'd guess that's a little aggressive for what you need; though I personally am a lot more comfortable with 4bbl carburetors, so that might work out in your favor if you know them. For sure the Offenhauser should be able to mate up to your existing exhaust manifold, so no need to run anything fancy. Linkages get complicated though. If you're not looking to make a lot of changes, I'd just look for another stock intake; anything for a 250 should fit it, I don't think the design changed (until the integrated head garbage)

 

[WamboJambo]

Also, I think that the earlier 230s and 194s also used the same intake setup. Don't buy anything based on that information though, not positive. If you look at Summit for their applications on the Offenhauser 5416 they suggest it'll fit a 194, 230, 250, and even a 292.

 

[JohnTaurus]

I've been doing a lot of research on this lately and the only ones I see commonly made these days are performance-oriented, and the big names are Offenhauser and Clifford. Both of them make single-quad barrel intakes and triple single barrel intakes, but I'd guess that's a little aggressive for what you need; though I personally am a lot more comfortable with 4bbl carburetors, so that might work out in your favor if you know them. For sure the Offenhauser should be able to mate up to your existing exhaust manifold, so no need to run anything fancy. Linkages get complicated though. If you're not looking to make a lot of changes, I'd just look for another stock intake; anything for a 250 should fit it, I don't think the design changed (until the integrated head garbage)

That's the information I was looking for, thank you again! I will expand my search to other years to see what I can find.

To anyone:
I know this would be easier with a more common engine, I'm certainly not oblivious to that. Lol! Just doesn't fit my goals for this truck.

 

[WamboJambo]

So I did a quick little search for your fuel injection thing, and I found a thread over at inliners about fuel injection on a 250, and Tom Lowe (of 12bolt.com fame, pretty big in inline stuff from what I've seen so far) suggested that you can toss a 2bbl Holley TBI kit on it, though it'd be a little overkill for the engine. Link to Holley TBI kit: https://www.summitracing.com/parts/HLY-700-21

Also, link to the inliners post for posterity: https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=64104

EDIT: sorry, should've checked my links first. That TBI kit is not only stupid expensive (>$1k), it's also not even available there anymore. Ignore me

 

[DoubleDingo]

I've been doing a lot of research on this lately and the only ones I see commonly made these days are performance-oriented, and the big names are Offenhauser and Clifford. Both of them make single-quad barrel intakes and triple single barrel intakes, but I'd guess that's a little aggressive for what you need; though I personally am a lot more comfortable with 4bbl carburetors, so that might work out in your favor if you know them. For sure the Offenhauser should be able to mate up to your existing exhaust manifold, so no need to run anything fancy. Linkages get complicated though. If you're not looking to make a lot of changes, I'd just look for another stock intake; anything for a 250 should fit it, I don't think the design changed (until the integrated head garbage)

Offenhauser would be good for what he is doing. Clifford is for racing.

 

[DoubleDingo]

So I did a quick little search for your fuel injection thing, and I found a thread over at inliners about fuel injection on a 250, and Tom Lowe (of 12bolt.com fame, pretty big in inline stuff from what I've seen so far) suggested that you can toss a 2bbl Holley TBI kit on it, though it'd be a little overkill for the engine. Link to Holley TBI kit: https://www.summitracing.com/parts/HLY-700-21

Also, link to the inliners post for posterity: https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=64104

EDIT: sorry, should've checked my links first. That TBI kit is not only stupid expensive (>$1k), it's also not even available there anymore. Ignore me

Tom Lowe knows his stuff.

 

[DoubleDingo]

You should be able to find I-6 intake and exhaust on craiglist or ebay. You may have to search many different times over a long span of time, but they do pop up. If I were you I'd get the Offenhauser as it uses the stock heat for the carb, so you can run stock exhaust or header. If you go with header then you need to plumb in heat for the carb.

When I start collecting power goodies for my 292 it's going to be Offenhauser intake, stock exhaust, 2.5 or 2.25 exhaust pipe through glasspacks. Yes glasspacks. A short resonator upstream, and a long one at the back. The head will be getting 1.84 valves and the lump kit. Then a quadrajet I have laying around will get recalibrated and jetted accordingly for the flow numbers of the head. It'll require an adapter plate to fit the Offenhauser, though. The lump kit with an increase in valve size moves the torque output up quite a bit, like a cam change. In concert with a cam change that also matches the flow numbers of the head and you have a very strong I-6. https://www.12bolt.com/65279inline-cylinder-head-flow65279.html

Granted the dyno chart shows the rpms being well above what you'd run you engine at for work or on the street, look at the torque curve down low at 2500-3000 rpms. Look how much it increased with the different setups.

 

[SirRobyn0]

I was going to do some quotes but it seems I missed a lot during the day today so it'll just be comments. I do not mind carburetors at all, though in a daily driver I prefer fuel injection simply because there is less maintenance, plugs last longer, no carb adjustments ect. However a properly tuned carb will run every bit a well as a EFI. I had a 1965 C-20 with a inline 6 about 25 years ago, I really enjoyed the 6 and if I had a square with a 6 I'd want to keep it that way. With that said mine has the 350 and I want to keep it that way, but I like a 6 too.

 

[1987 GMC Jimmy]

I was going to do some quotes but it seems I missed a lot during the day today so it'll just be comments. I do not mind carburetors at all, though in a daily driver I prefer fuel injection simply because there is less maintenance, plugs last longer, no carb adjustments ect. However a properly tuned carb will run every bit a well as a EFI. I had a 1965 C-20 with a inline 6 about 25 years ago, I really enjoyed the 6 and if I had a square with a 6 I'd want to keep it that way. With that said mine has the 350 and I want to keep it that way, but I like a 6 too.

Agreed. I used to feel like the OP towards carbs, but I’ve softened on them considerably where I’d seek out a carbed vehicle over even a TBI.

To the OP, I’m from and currently in sorta South Mississippi, too, but it looks I’m heading back to New Orleans soon. I think you’re on the right track, but I would recommend sticking with the divorced/electric choke setup and getting it right rather than going electric. Keep it simple if you can.

If you wanted to go with adding FI to one of these old stovebolt style engines, that might be a cool project. If I was doing that, I’d probably use a Rochester TBI setup from a 1982-90 Iron Duke motor, and you’d need the ECM and wiring harness from a 4.3. It’s a single injector 300 CFM unit, which I believe the 1MV is 250. You would need a 4.3 injector, a 3.1 injector would be a tad too small. The distributor is tricky, you’d likely have to figure out how to remotely run a TBI ignition module to a later 250/292 distributor assuming you run points now. A few people have run the full 2 bbl TBI units on hot 292s, but I think that’s overkill on a stocker 250.

 

[JohnTaurus]

Wow! Such good information, guys, I really appreciate your comments, suggestions, etc.

Time will tell, but using the TBI system parts from other GM vehicles sounds like a winner to me. The truck already has a new (stock-style) exhaust manifold, and it has a aftermarket electronic ignition (so, no points distributor). This will be another big step in making it a low-maintenance, worry-free daily driver.

 

[bucket]

If going the single barrel TBI route, the '87-up unit is much better than the earlier unit. A 2bbl unit shouldn't be overkill though? That's what I personally would choose. A unit from a 4.3 should work well, it's only 12 more cubic inches after all.

 

[JohnTaurus]

Yes, I like the idea of using a 4.3L throttle body. I will be doing towing and hauling occasionally, but the truck will be driven on the highway unloaded a lot, too. The injection, coupled with the 5 speed manual will make for an excellent, torquey and economical daily.

Again, this is future plans. Right now, I'm just trying to get it back to where I can comfortably drive it to work while my other vehicles are getting much-needed repairs. I'm fine with having a good-performing carburetor in the meantime.