Marvel MA-4SPA carb float adjustment ?

[GEM930]

I've searched the archives and even the web but have been unable to find any info on checking the float level on a Marvel MA-4SPA. Any ideas?
Thanks
GEM

[dhammer]

Take a look at http://www.esscoaircraft.com/Marvel_Schebler_s/226.htm
It looks like they have all the manuals on these carbs. The Maintenance/Service Manual for the SPA will cost you $21.00

[GEM930]

The carb is off now and I was hoping to install it today or tomorrow, as I'm taking a trip this weekend. If anyone can give me quick and dirty instructions to check the float level that would be great, if not I'll order the book and hold off on this weekends trip!
Thanks!
Gem

[dhammer]

I'm concerned,

Is there a reason you are worried about the float level? If you've had it apart, don't try and fly with it until you follow all the manufacturer's instructions for assembly and test. There are just too many ways, as simple as they seem, to screw one of these things up.

If I remember right, you have to have a go/no go gage and feed it fuel under a specified pressure then adjust the level with shims under the valve seat.

Don't be offended, but for your own safety do something for me. Get the book and follow it, or better yet send it to a good carb shop. I don't want to see another subject line here that says - "RV-? down in ????" and everyone wishing you God's speed while they wait for the NTSB report.

[GEM930]

No offence taken. Been fighting cht and oil temp problems....fuel flow was only 10.2 GPU wot / full rich. Engine is 0320 H2AD out of a 172. General consensus is running too lean. Jet diameter was .096, drilled to .0995. Just thought it might not be a bad idea to check float level as well.

[dhammer]

Thanks,

Maybe there is someone out there that has the service instructions they can share with you. Last time I messed with a carb was in A&P school in 1970.

Opening up the jets is a big no no for a lean engine. Either it's the wrong carb for your engine or something else is going wrong In other words, float levels may change as carbs age, usually because the seat wears, jet sizes don't. If the float level is too low and you correct that, you may or may not be too rich. Based on the now modified shape of the jet, it may never work properly again. Not all jets are straight through holes. Some are stepped or tapered. Any particular jet is designed for a particular engine and should not be altered.

Another thing to consider is the mixture is changed by varying the air pressure on top of the fuel in the bowl. A malfunction that system could be causing it to call for a lean mixture while rich is selected. That's another symptom of wear.

Like I said, they seem simple, but are actually pretty complex. For a good read check out http://www.kellyaerospace.com/articl...essory_AMT.pdf

Personally I get a good shop to repair it before putting it back on the engine.

Don

[ABRV4]

I've got the manual for the MA-4SPA somewhere at home as I used it when I overhauled my carb. If I remember right, setting the float level wasn't that big a deal. I'll find it this evening and then maybe I can scan in the pertinent pages and email them to you.

Alan
RV-4 N7028K

[ABRV4]

GEM,
Check your messages.

Alan

[GEM930]

got it thanks!

[n5lp]

Lopey idle after cold start unless I lean it almost to idle cutoff. Symptom disappears after running the engine awhile. Today I pressurized the fuel system to check for leaks after repairing another problem and find the carb is leaking fuel from the center seam.

Well I'm sure I'm not knowledgable enough to work on it so the problem is finding a mechanic from another town willing to come look at it.

Things were pretty trouble free for about the first 8 years.