Carb spacer

[Lahti35]

Pulled the GAZ out of winter mothball storage today so I could replace the front crankshaft seal, head temperature sender and install a carb spacer.

I've always had trouble with the gas boiling off from heat buildup under the hood. It was so bad you could see the gas percolating through the carb window

I tried a few types of gasket material, sometimes using multiple layered gaskets with little success. Today I made this one out of some phenolic sheet stock and am glad to report the gas in my carb no longer boils off. So if you're looking to fix your carb soaking up too much heat this material does work

[Geronimo]

Hi Lahti,
When assembling the engine I will also build in such a spacer, I've read so many stories about boiling fuel that it seems it is a common shortcoming of this engine. I found the original shielding plate for protecting the carb from the exhaust heat, but I have doubts if only this will do the trick:

Anyhow, looks like also our comrades knew the problem

[iannima]

Anyhow, looks like also our comrades knew the problem

They certainly did! And it is surprising that they did not try and do something about it... It is even mentioned in a 1970 dated test drive for an Italian motoring magazine (Gaz 69s were also exported to the West). I had continuous grief with hot starting until I replaced the original gasket (a bit of a joke...) with something thicker. I adapted this:
http://www.ebay.co.uk/itm/150738963733? ... _805wt_909
It is for a Weber. I had to enlarge the holes for the studs but did not have to change them. It has made a huge difference although, by the looks of it, it has now degraded a bit. I might have to replace it.
On the German forum they have used a material called Pertinax to redo the gasket, but I have never understood how to find it in this country.

[KarlJ]

I thought Pertinax was FR-2 PCB laminate? Would Tufnol be an option or would it not survive the high temps? Tufnol 6G/92 can be used up to 250degC.

[haymish]

phenolic sheet often used and works well.seriously fire resistant-not that carbs get that hot.seen plywood used and it works well .very good insulation and as only edge showing to world couldn't catch fire if it wanted too!
get bold put it on an inch thick spacer and get much better torque and throttle response from your beastie.

[KarlJ]

You can get Tufnol sheet from RS etc. Not the cheapest material though, about £85 for a 590x285x10mm sheet (so about £30 not from RS!).

You could get a stack of old PCBs instead They are normally FR4 rather than FR2, and 1.6mm thick. It would be a fairly simple thing to do a PCB design with all the copper taken off and the holes in the right places. Precision would be 0.1mm ish. If anyone wanted to go down this path I'd be happy to create the design files if someone can get me the dimensions. If it's a common size to all these vehicles we could get a batch made up. Some old PCB with the components bashed off would be a good test though (try to pick some without too much copper on, and two layer would be better than multilayer for insulation).

[Eastblock]

Pertinax is just a brand name for phenolic sheet. IIRC, someone on the German forum made a spacer from PTFE. That should be able to withstand the heat.

Available here:
http://www.directplasticsonline.co.uk/ (Tufnol is 35% cheaper here than from RS)

[Lahti35]

Hi Lahti,
When assembling the engine I will also build in such a spacer, I've read so many stories about boiling fuel that it seems it is a common shortcoming of this engine. I found the original shielding plate for protecting the carb from the exhaust heat, but I have doubts if only this will do the trick:

Anyhow, looks like also our comrades knew the problem

Well thats neat-o! are you going to keep that one the engine when you restore it? I think you should

@Haymish: The sheet I had was 3/4 inch that I split in two to make this one... I though about going the whole width but didn't want to cut a hole in my hood for the air cleaner Although maybe a RAM scoop would look sexy!

[haymish]

shame not enough room .cheapest gain in hp you will ever get is by just lifting the carb about an inch .no idea on gaz but on naughty v8 lifting the holly/weber normally produces around an extra 20-30bhp.if get clever and put a bit of a taper on the spacer can get another 10-15bhp on top of that!-and if tapered then gives you lotsa low down torque

[Onbevreesd]

Geronimo,

I noticed you have got the Jikov (3010?) carb mounted, that is the same as mounted on my GAZ and I have never had any trouble with boiling petrol, even in the original set up without heat shield. If you need any information on this carb let me know as I found some drawings and information (in Czech, however) on the web.

Regards,

Marc

[iannima]

shame not enough room .cheapest gain in hp you will ever get is by just lifting the carb about an inch .no idea on gaz but on naughty v8 lifting the holly/weber normally produces around an extra 20-30bhp.if get clever and put a bit of a taper on the spacer can get another 10-15bhp on top of that!-and if tapered then gives you lotsa low down torque

That sounds interesting... By taper you mean tapering downwards I presume, that is from narrower (carb end) to wider (manifold). An inch might be too much but the entire rig could go up a bit, probably by fitting longer studs.

[haymish]

with the taper you are after the venturi effect![big at carb base-smaller at manifold]
basically its a law of physics that if you constrict a flow -then it has to speed up.the principal of continuity if i remember right.it is the jet effect.in effect if you constrict a flow you speed up the flow .this has several advantages.obviously petrol/air mix arriving at valves at a higher velocity -but other advantages too. fuel air charge cools as it goes through the venturi so can carry more o2 and in doing so also cools the carb and your engine vacuum increases which makes engine more efficient[especially relevant for low compression engines that are reknowned for low vacuum]as the fuel/air charge is speeded up it also encourages better mixing of fuel and air so more efficient combustion[also significantly quicker combustion cos fuel particles much smaller so burn quicker]-its a win win situation if you got the space to fit a spacer.
its quite a trade sectret of the better engine tuners-and missunderstood by most cos getting into the laws of physics and most people think bigger holes means more power-when really you need a bit of constriction..most people just presume the large spacer under the carb is just insulation-but its more a case of its insulation as well rather than the primary reason!10% is the minimum improvement i would expect with an inch spacer with a couple of mm restriction[even just one mm taper probably produce 10%]. just an inch spacer helps but to get real improvements get a taper on it-cos more power but more importantly the taper produces the power lower down the rev range and helps the torque lots too.parallel sided spacers tend to increase top end power only.
doesn't eat more fuel-infact makes engines more efficient.think of a hose pipe with the tap turned on.just glugs out the end but if you restrict the end of the hose the glug turns into a jet but uses no more water than when just going glug! just same with the flow of air/fuel through your carb.

[Eastblock]

So in principle the same as what a velocity stack does, just at the other end of the carb.

[iannima]

Very interesting. I shall investigate how much room there is before the air filter starts hitting the bonnet

[iannima]

Sorry can I ask to elaborate a bit further on the theory? The exhaust manifold is different between the 2.12 and the 2.4 side valve engine in that the opening with which it connects to the carburettor is of a different size. In the 2.12 engine it is 33 mm. whereas it is 38 mm. in the 2.4 one. For some reason I have the 38 mm. exhaust manifold. The carburettor opening is however 33mm. (as they nearly all are in the K22 type of carburettor). What difference is in theory this going to make?

[Geronimo]

I noticed you have got the Jikov (3010?) carb mounted

No, no, I found this engine on a scrap yard looking for other parts. Then I noticed this shielding plate and the owner agreed to unscrew it and sell it to me. Looking at the side view of an engine in the Russian manual it was there originally, so I will mount it and see if it does any good.
My engine, a 2,12l, has a K124 carb, but thanks for the offer to help.

[haymish]

So in principle the same as what a velocity stack does, just at the other end of the carb.

yup eastblock.its like an internal velocity stack-accelerating the fuel/air mix as it leaves the carb.
matteo-so you got a carb with 33mm oriface sitting on a 38 mm hole?-if that the case your poor engine must have terrible gas flow from carb to manifold.ideally the fuel/air flow at least does not slow down as it leaves the carb[going to a similar sized hole- as in most carb/manifold type situations]-but in your case it drops straight into a cavern and will be slowing down immediately.the art of engine tuning/design is keeping the max flow possible from carb to the valves.just like the 'wonderful' design of the gaz 66 manifold you will be getting fuel falling out of the mix and puddling in the manifold!if you put in a spacer with at least a 1mm taper on you will undoubtedly speed up the delivery and improve the quality of the fuel air mix.-ergo improve your overall performance.
taking it to extremes[not that i suggest anyone does]-on v8 racing manifolds the carbs are perched on top of what looks like a mt vesuvius shaped bump in the manifold-they raise the carb about 3" so as to maximize the venturi effect!
another advantage of putting in a spacer is it increases the length of the inlet tract[distance from carb to valve]even though it speeds up the gas flow-because the distance to the valves is greater it tends to increase the time that the fuel/air mix has to mix properly-and encourages low end torque.if you shorten the inlet tracts then you get all top end /high revving engine-definitely not on the list of requirements for russkie beasties!

[Onbevreesd]

My engine, a 2,12l, has a K124 carb, but thanks for the offer to help.

You're welcome.

Thanks Haymish for the tutorial, very helpfull! Just to be sure: the taper is in the direction of the manifold, so like a V-shape?

[haymish]

yes .got to have smaller end at the manifold-wider end at the carb.so as to create a constriction.as air/fuel flows through constriction it has to speed up.if other way round it slows it right down

[Geronimo]

Sorry Haymish, but I'm not convinced of your theory. The carb gives a certain flow, let's cal it x m3/s. Now, if this flow goes through a certain section (m2) it will have a certain speed (m/s). Flow = section x speed. Considering a constant flow, then the speed increases at locations with a smaller section but decreases again at locations with larger section. The outlet section of the carb is fixed, the sections inside the manifold are also fixed, so the only thing you will obtain is an increase in speed in your tapered spacer but once the mixture arrives in the manifold chamber it will resume its original speed. I do agree with obtaining a better mixture and I also agree that a tapered spacer will reduce turbulence.