How Tight Should Accelerator Pump Plunger be in the Bore?

Joined
Oct 4, 2018
Messages
181
Location
Marietta, GA
I am trying to diagnose a no start issue and noticed that no fuel appeared to be coming out of the nozzle when the plunger is pushed down. I proceeded to remove the top of the carb and I noticed the plunger seems very lose in the bore. There is a lot of play at the top of the bore and the fit gets better as it goes down, but never really seems to get a good seal between the bore wall and the rubber seal on the plunger. Thoughts?

 

Pighead

Stop calling it an FJ
 
 
Joined
Aug 31, 2004
Messages
7,717
Location
Denverish
Rubber seal on the plunger? I thought there was more more of a leather wrap that went around the business end of the plunger.
Also, probably ought to mention what year carb that is...
 

Pighead

Stop calling it an FJ
 
 
Joined
Aug 31, 2004
Messages
7,717
Location
Denverish
Well, I assume a real expert will chime in shortly, but again, I think there should be more of a wrapper on that plunger. I would be preparing to find a good rebuild kit for that carb, new plungers are usually included. Just for fun, take a good look down that bore and see if you see any remnants of a prior wrap. Perhaps obstructing the outlet? Might answer a question or two...
 

GA Architect

SILVER Star
Joined
Feb 14, 2014
Messages
3,201
Location
Woodstock, GA
I am trying to diagnose a no start issue and noticed that no fuel appeared to be coming out of the nozzle when the plunger is pushed down. I proceeded to remove the top of the carb and I noticed the plunger seems very lose in the bore. There is a lot of play at the top of the bore and the fit gets better as it goes down, but never really seems to get a good seal between the bore wall and the rubber seal on the plunger. Thoughts?

If I recall correctly, the Hygrade carb kits still have the leather plungers? Note, I used the 791B kit when I rebuilt a '76 Aisan.
 
Joined
Oct 4, 2018
Messages
181
Location
Marietta, GA
Did you alert this Fellow about your question before posting here? Perhaps even alert this Fellow to this post?
Yes, I have but not heard back so was just posting to get opinions. I fully expect to hear back so am not trying to throw anyone under the bus.
 

Mark W

 
Joined
Jan 7, 2005
Messages
6,442
Location
The Greatland
That fit appears normal to me. if you have no/weak squirt from the accel pump the most common cause is a tiny piece of debris clogging the nozzle.

Mark...
 

Mark W

 
Joined
Jan 7, 2005
Messages
6,442
Location
The Greatland
Mark, is there no leather skirt, or wrap on a '71 carb plunger then?
All the F and 2F carb accel pumps had a leather skirt. Rubber in a lot of rebuild kits. I could not see from the vid that there was no skirt on that one. There should be and if there is not, then that is certainly not right.. The bore of the pump is tapered. The plunger fits looser at the top than at the bottom.

Mark...
 

Pighead

Stop calling it an FJ
 
 
Joined
Aug 31, 2004
Messages
7,717
Location
Denverish
Yes, in re-watching the video, I can clearly see a rubber ring, bit nothing below that.
 
Joined
Oct 4, 2018
Messages
181
Location
Marietta, GA
Yes, there is only a rubber thing, no leather. My assumption is the rubber/leather serves much the same purpose as a piston ring - creating pressure when actuated so a reasonably close/tight fit is necessary to function correctly.
 

reddingcruiser

Practicing for retirement
GOLD Star
Joined
Feb 23, 2011
Messages
3,381
Location
Redding, California
That looks like it was improperly manufactured. The rubber cup looks too high up the shaft. Even if it was leather it would be the same problem.
 

Pighead

Stop calling it an FJ
 
 
Joined
Aug 31, 2004
Messages
7,717
Location
Denverish
OK, I found an old plunger. and a new one I haven't used yet. They have the leather wrap, about the same size as your rubber wrap it looks like.
My old one fits in the bore about like yours does, kinda sloppy at the top but tightens up further down. Tapered bore as Mark mentioned. Maybe halfway down the plunger stops if I just drop it in...
So, the play at the top might be normal and your no spray problem lies elsewhere. Again, as Mark suggested.

20200222_100237.jpg


20200222_100440.jpg


20200222_100308.jpg
 

Mark W

 
Joined
Jan 7, 2005
Messages
6,442
Location
The Greatland
Your plunger is exactly as it should be. It fits just the way it should too.

Check the squirter jet for obstruction. 90%+ plus of all accell pump problems are from clogged squirter jets. If that is not the problem, check the rest of the pump system for obstruction. It is almost certainly the jet.

Mark...
 
Top Bottom