The Stovebolt Site Forums The Shop Area Engine Shop insulator block under Rochester carb

Well, here's another question that I hope you guys can answer. My 1951 1/2 ton has a Rochester carb on the 216 Thriftmaster engine. I'll be rebuilding the carb shortly. I notice that there is no insulating block between the intake manifold and carb base, just a gasket.

Am I missing this part or was it omitted some years? Also, the d#*@! heat riser is stuck, I've been trying to free it up with Kroil & the usual methods (tap, tap, wiggle, wiggle), no joy yet. Are these available in the aftermarket?

A spacer would have been on the truck from the factory but it is not needed. Some engines used a governor so the intake studs were too long without it. The spacer allowed common intake stud lengths.

You'll probably need to use heat to free up the riser. The butterfly is brazed and would need removed to install a new shaft. Don't know if anyone makes a replacement but you don't need one since you'll already have to remove the butterfly. Ream the intake and install brass bushings before reinstalling the shaft so a rusted shaft will not seize it in the future.

Actually, the spacer is needed. It contains some (I believe 2) vacuum ports that the carb needs for proper operation. The manifold does not have these ports in it.

Vacuum port is in the carb base, not the spacer.

I got my riser free by pounding it but not in the direction the valve would move. I pounded it to move the shaft in and out. - Scott

50GMC253-

I agree that the ports are in the carb base, but if you bolt the carb right to the manifold, the surface of the manifold will cover the ports. The spacer has "notches" cut out in it to open it up for manifold vacuum.

OK Tim, I see what you are saying. Looks like you have a nice setup. How do you like the YF? I'm using WA-1s but it will be a good while before they see any gasoline.

Love the YF. I should have done it years ago. It is much smoother operating then the Rochester BC I had. Maybe it was just my particular carb, but it had a bad mid-range lag. Anyway the YF is smooth up to as fast as I dare to push it. The only drawback is it seems to use more gasoline than the Rochester did. It is worth it to me, though.

Great to hear. When they run better a guy tends to enjoy and burn more gas! Rochester horror stories turned me to Carter. I would have YFs but CarbKing says WA-1s are much easier to syncronize for duals, and I'm no expert.

I thought that the spacer was to insulate the carb from the heat generated by the exhaust manifold being so close to the intake.

okay guys, i also want to know the answer to fredstev's question as my 53 gmc 228 1bbl rottenchester don't have a spacer either.
what does it do?
do we need one?
what happens if we don't have one and haven't had one for years?
mine seems to work fine without it although it does get pretty bad gas mileage.

don't recall if my 228 had that insulator or not - the 235's all do

considering that piece is actually called the carb "insulator", I'd expect it has to do w/ keeping an even temp in the carb body as Jim sez - I figger if GM put'em there it was because they thought spending the extra money was necessary for whatever reason, so I've never tried not having it there - definitely wasn't a "spacer" to take up the slack on long studs, as they would have just put shorter studs in - no wasted $$$$$$$$ on these ol trucks

OTOH I've never seen reference in any troubleshooting list to problems caused by not having one - prolly cuz they knew nobody'd be goofy enuff to leave it out!

Bill

i'd sure buy one too red58 if i can find out for sure if the 228 is supposed to have one. also, i'm gonna try knocking the riser loose also as i suspect it has a function too, even though as i've said, it seems to work fine frozen in place.
great froum and knowledgeable people!

As far as I know, the "insulator block" is to keep the intake and exhaust manifolds from transferring a lot of heat to the carb base. This would cause the gas in the float bowl to percolate under some conditions, and that ain't a good thing.

These insulator blocks are available mail order, seems that I've seen them in the Chevy duty and/or Bowtie bits catalogs.

Some one mentioned that they may be to compensate for the space required by the governor assembly as used in commercial vehicles. Maybe - does' anyone have a truck with a governor AND a insulator block?

By the way, after really close examination of my carb base, I do have an insulator block. It was just disguised by grunge and dirt. It looked exactly like the manifold casting.

Question about the YF vs. Rochester ? Do you have to modify the linkage or does the YF hook right up without a hitch?

The spacer does not take up for the "slack" because of the governor. The governor is about 4 times thicker than the spacer. The spacer does indeed insulate the carb, but it also provides those vacuum ports. GMC's may or may not have had one. I don't know. But, I do know that GMC's usually ran a Zenith carb which may have not had the vacuum ports in the base, thereby not needing the ports cut into the spacer. As was said earlier, if GM put it there, it was needed. Its not that expensive, I'd go ahead and get a new one and install it.

Buckaroo01-

The Carter YF is a direct replacement for the Rochester B/BC. When I installed mine, I didn't have to tweak the throttle linkage or the fuel line. Direct bolt-on.