The Big Fuel System Job

[Bad Obsession]

I have decided that I am going to do a bit of work to my fuel system. I have a feeling that the vent to the fuel tank may be clogged. I am going to check this out and try to clean it out to make sure it is clear. Not sure what a clogged fuel vent would do to the system but it can't be a good thing (I have heard that wasps will build nests in the vent area from time to time).

I am then going to take a screen out of the fuel tank on the pick-up line. This is something that I have heard about from my brothers with Catalina 34s. I am not 100% sure that this exists but I want to make sure that if I do have one it is removed because it is said to cause problems.

Next I am going to change my Raycor Filter. It is just about time so I will go ahead and get this done. When I re-fill the filter I will also hit the filter and the fuel tank with Diesel 911.

The reason that all this is taking place is that I noticed that my RPMs drop and when I fill the tank up they tend to go back up. They only drop by a few hundred RPMs but I also can't get more than 2700 RPMs according to the tach. I am not sure the Tach is correct but I just want to get these things done anyways to rule them out.

Anyone done anything like this?

 

[Roger Long]

Condsider replacing all your fuel and vent hoses if they are old. My engine picked up 1000 rpm WOT after I did this and actually ran faster with the lift pump turned off than it did before with the lift pump running. This was after replacing the last bit of original 1980 hose that ran to the engine bundled with a wiring run. It was either pinched or had degraded inside in a way that was restricting fuel flow.

 

[Alan]

Roger is right. Fuel and water hoses degrade from the inside out not the reverse. These hoses are made of layers and the internal layers can break away causing restrictions inside that could impede flow.

The other issue that could cause a drop in engine rpm's is air entering the fuel line from the suction side of the fuel pump. On this side no fuel leak will be visible but the air entering in tiny bubbles will cause rpm drop or engine shut down.

 

[sailingdog]

I'd third replacing the hoses. Doing a full job like this and not replacing the hoses is not what you want... make sure you get marine-grade fuel hose though. There is a significant difference between terrestrial (automotive) fuel hose and marine fuel hose, as the marine stuff is required to meet stricter standards.

 

[Scott T-Bird]

Hmmm ... I wonder if the wax that I inadvertantly plugged the fuel vent screens with is a part of my recent problems with loss of rpm ... I hadn't thought of that, thanks!

 

[RichH]

With your described symptoms its probably a very good idea to disassemble your entire fuel system and examine EVERY component, especially the 'rubber' components.

Have you in the past year or so added any so-called bio-fuel ????????.

Many of these so-called bio-fuels are incompatible with the old-fashioned neoprene and BUNA rubber compounds which is most probably the OEM rubber tubing, etc. in your system.
Since the 'price spike' of last year, 'mob'/shady sources, etc., were 'silently' selling/distributing fuels mixed with high percentages of 'reclaim' (old-cooking) oil that had/has a lot of organic acids (oleic acid, etc.) mixed in - also incompatible with neoprene, etc. The symptoms will be very swollen and soft looking rubber .... but you'll only see this on the INSIDE of the hoses, and 'surface' of the diaphragm of your lift pump.

From my postings on fuel systems, etc. some of you have noted that I've been deeply and professionally involved in filtration engineering. I will related that a lot of 'shyster-ism' has occurred in the past few years in the 'distribution' of such fuels (not from the refineries but some of the entities that are involved in 'private distribution', etc.)... and if you find such rubber/polymer degradation you should replace with a rubber that uses EthylenePropyleneDiamineMonomer (EPDM) or EthylenePropylene EPR) rubber as a minimum. EPDM and EPR will not meet current CG etc. specs., which STILL insists on the incompatible Neoprene, etc., so you may have great difficulty in finding 'compatible' rubber tubing, if indeed you find the degradation in your system. Industrial supply sources will have the EPDM.

Be sure to check out the internals of ALL the hoses and also the condition of the diaphragm in your **lift pump**.

Other than that, Id check for a 'slug' of biofilm (calcyx- massive bacteria/fungal colony) lodged somewhere in the 'piping', probably that has broken loose from the tank, migrated through the system (and is 'before' the Racors) and is now restricting the tubing. If so, its probably lodged near a 'connector' in the system, an 'elbow' or near the 'required 'tank valve'. Just run a soft wire through the tubing to insure that its clear. Its a DAMN GOOD idea to remove any so-called 'screen' thats attached to your tank's 'diptube'.

To lessen the possibility of 'air-leaks', you should 're-trim' the copper tubing joint where you use a 'compression fitting'. Compression fittings are a one-time-tighten device, you really should trim the copper tubing back whwere the 'ferrule' connects to the tube each time you 'retighten'. Flared connections are vastly superior to 'compression' fittings as compression fitting are NOTORIOUS 'leakers'. BTW - do not use teflon tape on these fittings; they are a metal-to-metal seal and Teflon tape only 'hides' the problem.


Hope this helps.

 

[Stu Jackson]

Also

check your fuel pump filter and make sure it's plumbed correctly: tank to Racor to fuel pump. Catalina plumbed 'em all wrong: tank to pump to Racor, which ended up clogging the small filter in the fuel pump. See: http://c34.org/bbs/index.php/topic,2515.0.html

 

[Glenn17467]

Did mine last spring, cleaned separator, new filter and new pump on my 84 C30 with the M25. Used the NAPA fuel pump as well as replumbed the line from tank to separator to pump as Stu suggested. The pick up tube did not have a screen.