Paul L

I am thinking of going with a 3/8" spacer under the carb to prevent the fuel percolation problem. Will the stock air cleaner still fit under the hood? Where can I get a longer choke rod?

magicv8

Straighten the choke rod or make a new one.

To check clearance, take about 3 feet of aluminum foil, crush it in to a 3 foot long 1 inch diameter shape and lay it in a curve around the outside edge of the air cleaner - then shut the hood.

When you open the hood the aluminum tells you the clearance. I would advise double drilling and tapping the LH motor mout to restrain the engine lift to about 1/8inch with a high strength bolt. Drill the hole so that the bolt head fits in the freeze plug recess above the motor mount. No one will see it there.

Worked for me - 10 -12 years and rolling :auto:

PS You can check the Details page of my home page (listed below) for pictures of the modified motor mount. The restraining bolt actually makes it possible to use the "correct looking" old style motor mounts that have no safety interlock. The bolt will hold the motor before any interlock can be engaged.


[Modified by magicv8, 7:32 AM 1/29/2004]

Paul L

Thanks for the comments! I will check for clearance after winter storage. I dropped by the local speedshop/Holley dealer this morning re the longer choke rod and his advice was to use a coat hanger....?

67L36Driver

"use a coat hanger" Or welding rod of the correct diameter. Use original rod as a pattern with the extra length in the straight (vertical) section. Most coat hanger rod is somewhat small.

66427-450

yes, use a piece of SS welding rod, BUT, it sounds like a band-aid fix to me?? (or.. treating the symtom, not the root cause). your car shouldn't need a spacer, I'd go after the real problem and leave the intake set up stock.

:thumbs:

Paul L

That is an option as the car runs fine as is. Just thinking of preventative maintenance. But you are right in a sense: if I don't have trouble, why look for it?

hot1corvette1

I had a percolation problem on my big block. Never could find out why.
Anyway, I put a Holley spacer and heat diffuser and it helped. But never completely got rid of the percolation. Ran perfectly all the time, so never worried too much.

PS...my hunch was that all of this alcohol in our fuel was allowing it to percolate at a fairly low temp

magicv8

Look at your heat riser valve. I gutted mine after the second one froze in the closed position. FI cars have a spacer to replace it.

66427-450

the point is, a well tuned 327-300/350 shouldn't need modifications such as these to run properly....... if you have a vapor lock issue you may need some "corrective manit/tuning", instead of "preventative" maint.

magicv8

Dunno. Some summer days the smell of boiling gasoline in the garage got in the upholtery of the other 2 cars - what you get unless you make mods. I put double gaskets with a stainless heat shield between them under my carb.

I have never had vapor lock problems, and the car runs fine - it's the smell of boiling gasoline I wanted to tune up. The heat shield and gutted heat riser cut it to about half of what it was. The carb still gets cooked on the engine at shutdown, but it is no longer touching the burner. It may be a change in fuel formulation that causes the smell or it may just be that - in the 60s - I didn't have a garage to keep the car in, and now it gets parked in an insulated wetherstripped garage. The two Pontiacs that share the garage have a vapor recovery system.

Paul L

That is basically the issue with me. The 1967 runs well but stinks of gasoline. I sold a 1979 to buy it and the C3 was fume-free. The C2 has a constant smell to it. Perhaps I should get used to it but it is very annoying. I had hoped a spacer would help.

StrayDog

Use the copper wire thats in common wiring ( the wire in your home wireing ) u can use a razor balde & cut the copper piece free & its great to work with & will give you the oppertunity to experiment for correct length , coat hanger wie is to stiff & unforgivuing to work with................it worked for me. Woof the Dog :seeya :steering: :flag Note Holley has a heat shield, made from alum & will keep heat from radiating from intake to carb, sold by many venders including Summit & Jegs, its not thick enought to case clearence problems. :cheers:


[Modified by StrayDog, 9:46 AM 2/1/2004]

lars

Paul -
On a Holley, the fuel boiling/percolation is not caused by heat going up through the throttle body of the carb - a spacer will not solve your problem. The heat gets into the carb from radiant heating coming off the intake manifold and hitting the low-laying accel pump housing. This causes the fuel in the accel housing to boil, and it will discharge right out of the discharge nozzles. This will flood the engine after shutdown and cause the fuel odor you refer to. The problem is common now with the modern fuels with alcohol additives: these modern fuels have a lower boiling point than the "old" fuels.

To prevent this, intall a thin reflective shield between the manifold and the carb - the shield needs to extend out beyond the float bowls to prevent radiant heat from hitting the bowls and the accel pump. Holley sells these as a kit with various thickness gaskets. I make my own out of stainless or aluminum. Use the shield with the thin gaskets on both sides and you won't have a hood clearance problem, yet the percolation will be solved. We run these shields on all the CCC cars out here, and they work.

If you do need to make a new choke rod, get a "stick" of 1/8" diameter stainless steel welding rod. These make beautiful carb linkage pieces. The rod will bend at very sharp angles (put it in a vice, bend it, and smack the bend with a hammer to get a sharp 90-degree bend - the rod won't break or crack). Cut the ends with a hack saw and file smooth. You can make a Jesus-clip groove in the end by filing a groove with a Swiss file. Polish the rod on a wire wheel when done, and you have a custom rod that looks like the factory made it. I make Q-Jet rod linkage pieces (accel pump and choke pulloff rods) all the time from this stuff, and it works great.


[Modified by lars, 4:06 PM 2/1/2004]

Paul L

Thanks Lars,
I bought the Holley heat shield supposedly for the 4160 carb. It interfered with the gas-line, rear manifold vacuum fitting, crankcase vent tube and L-79 t-stat housing. After cutting and bending for several hours I just turfed it. Those units must be for modifed cars. I am still considering my options. This pic shows my intitial bend to clear the rear vacuum fitting. It was downhill from there.






[Modified by paul67, 6:59 PM 2/1/2004]

67wave_saver

Paul67

I have the same problem you do with the Holley crab. I installed a ½ inch MOROSO phenolic spacer with gasket and it cleared the stock hood with the stock air filter. Replaced the hood since then with a BB hood so I obviously do not even come close now. I used a coat hanger to make the choke rod. Made it exactly ½ inch longer than the original and it works great. Shaped it just like Lars mentioned. HOWEVER, the Holley still leaks after shut down. But O-MY, I gained all that extra horse power....The only thing it seemed to help was I do not have any more hard starts from the engine flooding. I talked to other 67 Vette owners with the same carb problem. One corrected the problem by lowering the float level by about ¼ inch. Another solved the problem by machining the warped metering block. Some say using a jig is safer than machining. I think mine comes from warm throttle shaft bores. One of these days I am going to have my throttle shafts re-bushed. The fuel must be leaking past the metering plate, then falling down onto the throttle plates. From there it is leaking past the throttle shafts which probably does not fit correctly in their bores any more. I think most Hollyes can be brought back to life by a good seasoned Holley mechanic which I am not. Until then, what I do now is let the engine cool down, stuff a paper town under each side of the carb. Next day I remove the two fuel stained paper towels. This keeps my Intake manifold from staining. Let us know if you solve the problem and good luck


:seeya SAVE :seeya THAT :seeya WAVE


[Modified by 67wave_saver, 8:50 PM 2/1/2004]


[Modified by 67wave_saver, 8:53 PM 2/1/2004]


[Modified by 67wave_saver, 8:55 PM 2/1/2004]

lars

Paul -
The Holley heat shield requires extensive modification typically. I usually shear off at least 3/4" to 1" of the forward edge, a 1/2" off the fuel line side, and a 1/2" off the back edge. The main idea is that you have some reflective shield remaining under the accel pump area and directly below the fuel bowls. Don't be shy about cutting the shield to fit - get some tin snips and chop it up..!

ctjackster

the GM-produced heat shield fits much better. I will post up a pic of it when I get home tonight.

Paul L

Thanks. If it has a part number on it I would appreciate that also.

ctjackster

will do of course, but I am not sure if it is currently being produced (I vainly searched the pn# myself once before asking a gentleman to part with one in his supply), but stock may exist. I got mine from a VERY KIND fellow who posts here every so often, and more so on the NCRS board. Even if not available, perhaps I could trace an outline of it and create some sort of .pdf or Word file of it. Hacking up the Holley version is also an option, of course.

edit -I just checked my records and John Hinckley idenfied it on another board as GM p/n 3969835. I'll see what the unit has on it as well.

and here's a post from an S-10 forum, seems to indicate the part is still available:

"RANDY406
I was looking back through the thread,When said you were using a heat diffuser did you mean the stacked combo of plates and gaskets or an actual heat shield?GM and Holley both make a heat shield it's approx. 13" long and 7" wide.The shield will deflect the radiant heat around the carb instead of through it.They are available in spread or square bore.The GM part # is 3969835"



[Modified by ctjackster, 12:05 PM 2/2/2004]

Paul L

The Holley shield mods did not work out to my satisfaction. In other words I butchered the darn thing. So if anyone has the GM version for sale please e-mail me.

The 3969835 number is still good in the GM database but my friends at GM where I used to work say no stock in Canada right down to the dealer level.