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Fuel pump question

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61frogeye

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I am going to be putting on a set of rebuilt SU-H1's on my stock 948 soon. The car is very hard to start when it is cold (no matter the air temp). While I am at it I thought it might be a good idea to replace the mechanical fuel pump with a new or rebuilt unit, might help the cold start problem? The one on the car is, as far as I can tell, original.

What do you think, good plan or run some tests first? How do you test these things? Are the new ones offered by Moss a worthy replacement? Anyone got a NOS or good rebuilt original they want to sell?

BTW, I did a compression test today and I was pleased to find this: #1 cyl-155, #'s 2,3 and 4-160. I have only had the car 3 months, with #'s like this should I assume the engine was probably rebuilt not that many miles ago?
 
It sounds like you have a perfectly good fuel pump but your carbs drain (drip).
Your fuel pump only works when the engine is turning (obviously) and it needs to fill (or close) the carb bowls before you can get the car running.
When you put on the new carbs I will bet that your problem will lessen tremendously but will never go away completely since fuel does evaporate if it doesn't drip.
Try the carbs first and then look at the pump.
BillM
 
Dave,

I'm pretty sure I have an NOS one of you are interested. You can email me off list.
 
More info: the idle is erratic also. In doing some research on the problem I found that a tired fuel pump could be to blame. When the car is warm and I stop at a light the idle varies between 800-1200. If I blip the throttle when it is at 800 it usually hangs at 1200 afterward unless I am at idle for quite a long time then it falls again. When I slow down after cruising at 60 the idle is usually high.

There is no obvious sign that the carbs are dripping, and this problem occurs on every cold start even if it is just 24 hours since last use. It always warm starts fine even after hours of being off. I will further investigate dripping carbs.
 
Idle is erratic With worn shafts too. I'd suggest one thing at a time - do the carbs, try it, then the pump if stilll necessary.
 
BTW those compression numbers are very good and yes, do suggest recent engine work. congrats!
:cheers:
 
Yes thanks, that really made my day. I also found out today that my heater blower works fine, the diverter flap cable is hooked up so the flap is working backwards. That should be an easy repair. All in all a very good day!
 
61frogeye said:
Yes thanks, that really made my day. I also found out today that my heater blower works fine, the diverter flap cable is hooked up so the flap is working backwards. That should be an easy repair. All in all a very good day!
Click to expand...

You just reminded me of my old '61 Mercury Meteor - in Saskatchewan - in winter (early 80's) I had quilts a plenty as it had no heat in winter - turns out the cables were reversed - heat on/off and vent up/down. (oops) and yeah, my fault. :wall:

On the bright side the woman next to me snuggled closer - and 27 years later we still do. :laugh:
 
It sounds like you may be running a bit too lean at idle, perhaps due to worn shafts or bushings. Have you tried to fatten it up a flat or two?
 
OR, the idle is not closing the carbs down as the return springs are not quite tight enough.

Check and see if you can push the throttle shaft closed a bit more with your finger when it is idling high. Not an unusual prob and easy fix.
 
Thanks guys,
A couple of weeks ago I sprayed some carb cleaner at the shaft/bushing area as a test and the idle did change momentarily, I am pretty sure it dropped at least on the back carb so the bushings are suspect. I have not adjusted anything on the carbs except the idle since purchasing the car.

I don't know if this is a coincidence, but when I did a compression test recently the plugs in cylinders #1 & 2 looked excellent, uniformly light tan overall on the electrodes and the ceramic was also just slightly tan. #3 & 4 plugs looked too rich to me.

I need to do a valve adjustment and then check the timing, then I will fiddle with the carbs after all of that is done. By that time my rebuilt set should be ready to go on.
 
BTW, static timing on a stock 948 should be 5 BTDC from what I have read. I have not yet been able to find what timing at idle should be set at.
 
5 degrees at idle or static, same.

Carb throttle shafts have no bushings. the brass rod wears and the carb body will typically be fine. Just replace the leaker with a new one.
 
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