tomjensen

Making a carb switch 32/36 to a 38/38.

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38 minutes ago, Mark92131 said:

The Canon manifold opening should not need modifications to clear the throttle plates on the Weber 38/38, the opening is bigger than the peanut 2-barrel stock intake manifold.  I would still consider using a phenolic spacer to reduce the chance of vapor lock.  The phenolic spacer may need some modification to match the larger opening on the Canon.

thank you sir.

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31 minutes ago, Mark92131 said:

 

 

The phenolic spacer prevents heat transfer between the carb and the intake manifold, which reduces the chance that the gasoline in the float bowl will vaporize from liquid to gas causing vapor lock in the fuel delivery system.

 

Mark92131

 

 

Where in the fuel delivery system does the vapor get locked?

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54 minutes ago, Jimmy said:

Where in the fuel delivery system does the vapor get locked?

 

From Wikipedia:

 

Vapor lock was far more common in older gasoline fuel systems incorporating a low-pressure mechanical fuel pump driven by the engine, located in the engine compartment and feeding a carburetor. Such pumps were typically located higher than the fuel tank, were directly heated by the engine and fed fuel directly to the float bowl inside the carburetor. Fuel was drawn under negative pressure (gauge pressure) from the feed line, increasing the risk of a vapor lock developing between the tank and pump. A vapor lock being drawn into the fuel pump could disrupt the fuel pressure long enough for the float chamber in the carburetor to partially or completely drain, causing fuel starvation in the engine. Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine.

 

Carburetor units may not effectively deal with fuel vapor being delivered to the float chamber. Most designs incorporate a pressure balance duct linking the top of the float bowl with either the intake to the carburetor or the outside air. Even if the pump can handle vapor locks effectively, fuel vapor entering the float bowl has to be vented. If this is done via the intake system, the mixture is, in effect, enriched, creating a mixture control and pollution issue. If it is done by venting to the outside, the result is direct hydrocarbon pollution and an effective loss of fuel efficiency and possibly a fuel odor problem. For this reason, some fuel delivery systems allow fuel vapor to be returned to the fuel tank to be condensed back to the liquid phase, or using an active carbon filled canister where fuel vapor is absorbed. This is usually implemented by removing fuel vapor from the fuel line near the engine rather than from the float bowl. Such a system may also divert excess fuel pressure from the pump back to the tank.

 

A vapor lock is more likely to develop when the vehicle is in traffic because the under-hood temperature tends to rise. A vapor lock can also develop when the engine is stopped while hot and the vehicle is parked for a short period. The fuel in the line near the engine does not move and can thus heat up sufficiently to form a vapor lock. The problem is more likely in hot weather or high altitude in either case.

 

Mark92131

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40 minutes ago, Mark92131 said:

 

From Wikipedia:

 

Vapor lock was far more common in older gasoline fuel systems incorporating a low-pressure mechanical fuel pump driven by the engine, located in the engine compartment and feeding a carburetor. Such pumps were typically located higher than the fuel tank, were directly heated by the engine and fed fuel directly to the float bowl inside the carburetor. Fuel was drawn under negative pressure (gauge pressure) from the feed line, increasing the risk of a vapor lock developing between the tank and pump. A vapor lock being drawn into the fuel pump could disrupt the fuel pressure long enough for the float chamber in the carburetor to partially or completely drain, causing fuel starvation in the engine. Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine.

 

I'm quite familiar with the legend of vapor lock. I was asking specific about a 32/36 installed on an M10 in a 2002. A phenolic spacer has no relevance to the above scenario.

 

40 minutes ago, Mark92131 said:

Carburetor units may not effectively deal with fuel vapor being delivered to the float chamber. Most designs incorporate a pressure balance duct linking the top of the float bowl with either the intake to the carburetor or the outside air. Even if the pump can handle vapor locks effectively, fuel vapor entering the float bowl has to be vented. If this is done via the intake system, the mixture is, in effect, enriched, creating a mixture control and pollution issue. If it is done by venting to the outside, the result is direct hydrocarbon pollution and an effective loss of fuel efficiency and possibly a fuel odor problem. For this reason, some fuel delivery systems allow fuel vapor to be returned to the fuel tank to be condensed back to the liquid phase, or using an active carbon filled canister where fuel vapor is absorbed. This is usually implemented by removing fuel vapor from the fuel line near the engine rather than from the float bowl. Such a system may also divert excess fuel pressure from the pump back to the tank.

 

Again, this references a scenario where vapor is introduced into the carburetor by the pump, a scenario a phenolic spacer won't prevent. So far the only example provided is with the float bowl, and 32/36 carbs have float bowl venting incorporated into the design, I presume 38/38 do as well given the similarity.

 

40 minutes ago, Mark92131 said:

A vapor lock is more likely to develop when the vehicle is in traffic because the under-hood temperature tends to rise. A vapor lock can also develop when the engine is stopped while hot and the vehicle is parked for a short period. The fuel in the line near the engine does not move and can thus heat up sufficiently to form a vapor lock. The problem is more likely in hot weather or high altitude in either case.

 

Again, this references a creation of vapor in the line prior to being delivered to the carburetor. 

 

40 minutes ago, Mark92131 said:

Mark92131

 

So the takeaway as that as long as your fuel lines are routed correctly, or if they're routed incorrectly but your carburetor has bowl vents that aren't blocked, vapor lock isn't a problem anyone needs to worry about.

 

Thanks!

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I ended up going with a new 38/38 from Pierce Manifold in Gilroy. Thanks for all the input.


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22 hours ago, Jimmy said:

vapor lock isn't a problem anyone needs to worry about.

 

Apparently, BMW worries about it.

 

Mark92131

 

13111266764

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I think I found the culprit to a few issues I was having including the cabin smelling like gasoline.86c503ad87c4e7cad729d45a873a8caa.jpg


Sent from my iPhone using Tapatalk

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On 2/5/2019 at 12:42 PM, Mark92131 said:

 

Apparently, BMW worries about it.

 

Mark92131

 

13111266764

 

I know they located the fuel line with the ac line on the E30. Did they ever use phenolic between the intake manifold and head on the M10? I see the fuel pump has one.

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59 minutes ago, Jimmy said:

 

I know they located the fuel line with the ac line on the E30. Did they ever use phenolic between the intake manifold and head on the M10? I see the fuel pump has one.

 

BMW put a phenolic insulator between the carb and manifold on every type of carb on the 02 (single barrel Solex, twin downdraft Solex and Solex 40PHH sidedrafts)

 

I think the issue they are trying to protect against is fuel boiling and percolating out of the float bowl rather than ‘vapour lock’ per se. 

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There was even an optional E30 fuel cooler that had a little evaporator that pulled from the A/C system...

Meant for the Middle Eastern market, iirc.

 

we watched fuel boil in a fuel cell in Portland one hot afternoon- the temps in the trunk were over 140f.

 

t

 

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On 2/3/2019 at 1:40 PM, tomjensen said:

I agree. What’s weird is that when I went the buy a new K&N air filter, nothing fit. The new air filter was a little too tall and the cover wouldn’t fit. Could get the retaining screws started.

 

Somebody on the forum had this setup for the air filter. I'm considering it as I would like a little more hood clearance. Seem's like it may breath a little better also. 

You need: 

ITG Custom Base Plate 3JC20

Air Filter JC20 or the higher flow filter depending on budget

https://itgfilters.net

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I have an ITG filter. It fits both the 32/36 and 38/38. It works great. Clean it with soap and water every once in a while and spray it with filter oil and you're good to go. No stupid that clips to rattle off either. 

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