R1 avanti rpm surges at high rpm

[Pmaenner]

Hi everyone, 

    New owner of an 1964 r1 Avanti.  Had a question on diagnosing an issue I discovered.  

      First thing I noticed was that it Had trouble going up my very steep driveway.  Had to get on level ground, and gun it so that it could make it up.

   I replaced the fuel and air filter.  It has the old glass bowl type.  I noticed it took awhile for the filter bowl to get filled with fuel.  It was hard to fire up initially. but once it did, it had no problem restarting.  After I replaced the filter, no problem getting up my driveway.  I did notice some sediment in the bottom of the bowl.  It looks clean now after replacing the filter.

     Warmed the engine up and revved it in park, no problem hitting 6k.   I took it for a test drive and noticed up to around 3500 rpm, I had no issues.  When I tried to go faster, the rpm would flutter around.  I'd hit 4500, then it would drop to 3700, back up to 4500, then drop to 3700 or so.  Only time this wasn't an issue was when I was on a slight downhill and it accelerated smoothly up to 5k before I had to slow down.

   I'm thinking it's the fuel pump starting to go.  I know the issue could be several things, but in your experiences, where else should I be looking?  Also, on a different note, what should my vacuum gauge be reading at idle for an R1?  On the studebaker axles, how do I tell if it has the twin traction option?  When I swapped wheels, I noticed it behaved like an open differential.  Just curious if that is the way it came or the clutch packs are burnt out.

   I was told the carb was rebuilt a few years ago, the transmission serviced and the engine tuned up.  The engine is original and has never been rebuilt.

  Only things I've done is new tires and wheels, put my vacuum advance on manifold vacuum, and been trying to fix a leak on my coolant surge tank.

   I appreciate any advice or insight you guys and gals may have!

 

-Pete

[studegary]

Hopefully, you are not trying to run on some old fuel (more than three months old).  Other than that, it does sound like a fuel delivery problem.  It may not be the pump.  It could be a restriction at the tank exit, a pinhole leak in a line sucking in air, a restriction in a line, old style fuel hose that has expanded internally, etc. 

[Pmaenner]

Thanks Gary!

   I put fresh gas in there, put in 93 which is the best I can do locally before in took it on my test drive.

   I did search for vacuum leaks. Didn't find any.  Didn't see any leaks from the fuel line, fuel hoses look to be in good shape. 

    I'll disconnect the lines at the tank and see what it looks like.

 

-Pete

[Avanti83]

I agree with looking at fuel issues for starters but the other Issue I always look at when losing power under load is timing and advance. Be sure the plugs, points and wires are good and put a timing light on it to look at both initial and advance when it's warmed up.

Also be sure the secondary's are opening and you have fuel from the accelerator pump. 

[Pmaenner]

Good point.  I checked initial timing, it's set at factory 4 degrees.  I didn't check the advance, I'll take a look at that too.

 

-Pete

[Pmaenner]

Checked the lines, didn't see any issue.  Advance is working, looks like I got about 22 degrees mechanical advance, which jives with the shop manual.

   Funny thing, test drive today and I couldn't get it to surge like it did before.  On one acceleration it may have lost a little rpm around 4500, it was hard to tell.  Rest of the time I didn't notice anything.  I was shifting around 5k.  I'll test drive it again when I get a chance, see if the problem re-emerges.

    I doubt the fuel pump fixed itself.  I'm thinking now, old fuel or dirt in the fuel lines.  I had about 1/4 tank of old fuel when I filled up.  I thought filling up with fresh would be all-right.

     I'm at 4 degrees on initial timing.  I plan to bump that up in 2 degree increments until I find what works best for me.

    Other than that, I'll be getting the coolant surge tank kit from SI.  And replacing the glass bowl filter with an inline one.

 

-Pete

[studegary]

Not removing/replacing the old fuel may have caused your problem.  In cars, especially those without a sealed system, modern fuels go bad rather quickly.   Now that it is mixed up, you may need to run a couple of tanks of fuel through, unless you want to empty the system and start over.

[Pmaenner]

Hey everyone,

 

    Just putting up an update here.  Been a little busy, but the surging was annoying me so I dived into it a bit more.  Looks like the fuel pump is degraded.  I hooked up a pressure gauge, was reading 4-4.5 pounds at idle.  When it warmed up, pressure reading dropped to around 3.  Noticed on the hard acceleration, the pressure dropped down to 1 pound, but would recover back to 3 when the rpms came down.  Did a suction pressure test and got around 4-5 inches of vacuum.  Shop manual says I should be expecting 5.5-7 pounds on the fuel pressure and about 10 inches of vacuum on the suction pressure.  I also went through the carb, make sure nothing was sticking with the floats and everything looked good there.  So even with any inaccuracies in my gauges, I think the fuel pump is the issue.  I'll be replacing that when I get a chance and see what happens.  I'm thinking the fuel pump was operating right at the threshold of decent performance, hence why sometimes I got the surging and other times I didn't.  I also noticed that when I plugged the vapor return line off of the filter, the engine ran better too.  I haven't been getting any vapor lock, so I'm gonna replace the filter with a normal inline without a return line.  Hopefully this'll fix the issue!

[brad]

The is no "Vapor" return line off any Studebaker filter. It would be a "fuel" return line, which should be restricted to a .045" then it returns to the fuel tank. If you have an aftermarket filter, AND the return line fitting at the fuel pump, then there is your low pressure problems. Also the vacuum metering rod springs might be too weak, and leaning out your engine at steady high vacuum conditions. Often rebuilders "mess " with things and get them out of whack.

Also, nobody has mentioned the Prestolite distributor mechanical advance. They are notorious for wear, and sloppy advance results. The solution is Chrysler Prestolite weights with bronze bushings. They need to be from a big block Chrysler as they have the correct counter-clockwise rotation. Although you can press the weights advance pins through on small block weights, and mount them upside down as the spring attachments are countersunk to about the center of their width.