Home 
Home Search search Menu menu Not logged in - Login | Register
> Jensen Healey & Jensen GT Tech > Carburetors > Rebuild or upgrade?

 Moderated by: Greg Fletcher
New Topic Reply Printer Friendly
Rebuild or upgrade?  Rate Topic 
AuthorPost
 Posted: 12-17-2018 02:14 pm
  PM Quote Reply
1st Post
JGriff
Member


Joined: 11-21-2018
Location: Boston, Massachusetts USA
Posts: 12
Status: 
Offline
I’m a newbie to the JH world so forgive me if this is a rookie question.
My new to me Jensen has about 66k miles. I have some service history on the car over the last 5-6 years but it appears the Strombergs on it have not been worked on in a while. The car is running OK but a little rich which I need to track down why. It has an aftermarket fuel pump (Mr. Gasket 42S Electric Fuel Pump) that was recently installed so I’m wondering if that is contributing to the running rich. Any thoughts on this?

Anyway I feel the carbs probably should be rebuilt. They look like they haven’t been touched in a while and I’ve noticed both seem to be leaking a little which sounds like a big fire hazard. I would send them out to someone for a full overhaul and not try to do them myself. The question I have is would this be a good opportunity to do a Dellorto conversion? Is going to a Dell 45s that big of an upgrade?

Thank you.

Back To Top PM Quote Reply  

 Posted: 12-18-2018 02:03 pm
  PM Quote Reply
2nd Post
Frank Schwartz
Member
 

Joined: 02-18-2011
Location:  
Posts: 300
Status: 
Offline
If I am not mistaken, that fuel pump, and others of similar make, are supposed to be used with a fuel pressure regulator, You can buy one at most car part stores for about 20 to 25 dollars and you set it at 2.5 pounds. If this does not fix the excess fuel going into the carbs and making it run rich, then the carburetors may be set a bit rich. Look in your manual and see how to set the carbs a bit leaner. Also check for any air leaks in all the hoses connected to the manifold and carburetors. I am of the old school of "if it ain't broke, don't fix it" so if the carbs are working ok and not leaking any gas off the bottom of the bowls (an easy fix) and all seems ok, then maybe it is only the needle settings..
Let us know your progress..
Frank

Back To Top PM Quote Reply

 Posted: 12-18-2018 03:34 pm
  PM Quote Reply
3rd Post
Sander
Member


Joined: 03-15-2005
Location: Peachtree Corners, Georgia USA
Posts: 77
Status: 
Offline
I'm not sure what you consider "rich"
but understand that President Trump has signed an
Executive Order that extends the use of E15
(15% ethanol)from just in the winter months to year round.
The original theory was that it was restricted
from use from June until September because they thought
that it added to smog concerns, which seems
counter intuitive to this non expert because it is
an oxygenate to reduce emissions. Anyway be
aware if you start seeing it at the pumps. E10 is
bad for our old cars and engines and E15 is even
worse. If you are forced to use it and you are using
a gasoline additive such as Driven Gasoline
Defender it will continue to give you the same
protection in the original recommended dose.
What you do need to take into consideration
is that it will cause your engine to run leaner and
you may need to richen the carbs. Once again, E10
gives a leaner burn than non ethanol gas and E15
is even more lean. Just a word of warning.

Some say there's no "improvement" switching to
Weber or Dellorto carbs unless you've upgraded
during engine rebuild (crank, cams, larger pistons, etc.)
and could actually lose performance by the costly swap
without those upgrades. I'd wait for others to chime
in on this and simply rebuild your Strombergs for now.

Back To Top PM Quote Reply  

 Posted: 12-18-2018 04:11 pm
  PM Quote Reply
4th Post
JGriff
Member


Joined: 11-21-2018
Location: Boston, Massachusetts USA
Posts: 12
Status: 
Offline
Thanks everyone for the input. I tend to agree it may be best to just fix what is needed than going down a rabbit hole putting a whole new intake and carbs on it possibly creating bigger problems. Keep it simple.
However I do suspect that the aftermarket fuel pump is contributing to the issue. Does anyone have experience with the solid state Facet unit Delta offers? Or the solid state SU from JHPS? I think I'd rather replace the pump than adding a regulator.

Back To Top PM Quote Reply

 Posted: 12-18-2018 05:54 pm
  PM Quote Reply
5th Post
Frank Schwartz
Member
 

Joined: 02-18-2011
Location:  
Posts: 300
Status: 
Offline
If you can, measure the pressure at the carburetor feed (T) and if it is more than 2.5 pounds...again...get a pressure regulator..they are cheap

Frank

Back To Top PM Quote Reply  

 Posted: 12-19-2018 03:58 am
  PM Quote Reply
6th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 386
Status: 
Offline
Constant Depression carburetors, like Zenith-Strombergs & SUs don't have the crisp throttle response that's typical of a venturi carb. Opening the throttle starts a series of events that ultimately causes the piston to rise, lifting the tapered needle out of a fixed jet. All that happens rather quickly, but not as fast/ nearly instantly as in a venturi carb. There, the throttle opens and end of story... you're going.

Disappointment is a function of expectations. If you want a better throttle response in your sports car, and the ZS carbs aren't giving it to you, then you might appreciate a set of Dellortos. But ZS carbs can also be tuned for power instead of emissions, and a well tuned, lightly hotrodded engine on ZS carbs can put out very nearly the same peak power as a Dellorto carbed engine. But, the ZS carbs will still have that more lethargic throttle response. Power and sporty are not synonymous.

To this point, you haven't said your goal is more power. The emissions carbs in an original state of tune should be lean, yet you're complaining that they're rich, and leaking. If that's the only problem, then fix it. And part of the fix may well be getting the fuel pressure down to 1.5 to 2.5 psi.

Dellortos will also run rich and possibly leak if fed with too much pressure. "IF" there's a presssure problem, Dellortos won't necessarily fix it.

It's easy to check the fuel pressure at the carb inlets. If it's over 2.5 psi, fix it. If it's under, then the mixture and leaking problems are probably in the old carbs, service them.

Dellortos aren't really a factor here... they're not a 'fix'. But if you 'want' Dellortos, then convert to them now, before you sink money into the Strombergs. That decision is a 'want', not a 'fix'.

Good luck,
Tim Engel

Last edited on 12-19-2018 04:03 am by Esprit2

Back To Top PM Quote Reply

 Posted: 12-19-2018 05:50 am
  PM Quote Reply
7th Post
Tom Bradley
Member
 

Joined: 07-15-2013
Location:  
Posts: 136
Status: 
Offline
If the carbs are leaking, they probably need some work, if only new gas inlet valves. Running rich could be caused by the Mr Gasket fuel pump, but it should not cause leakage. The pressure on the one I had was only slightly high: 3-4 PSI. But I never really liked it and finally replaced it with a Facet (from Amazon, I don't trust anything from Delta anymore) which runs at 2-2.5 PSI so doesn't need a regulator. This is the type of pump I have always had on the car and never had any problems.

If you send your carbs out for rebuilding I would suggest apple hydraulics: I had a pair rebuilt there years ago that worked well. But the ones I recently sent out to Joe Curto took forever to get back and had issues I had to solve for myself.

Back To Top PM Quote Reply  

 Posted: 12-19-2018 12:05 pm
  PM Quote Reply
8th Post
JGriff
Member


Joined: 11-21-2018
Location: Boston, Massachusetts USA
Posts: 12
Status: 
Offline
Thank you everyone for the replies. I appreciate that the community is so welcoming and willing to help me sort things out. It's helping me come up with a plan.
First off I need to fix the leak on the rear carb. Seems to be coming from the bottom plug. It just pulls out to replace the O ring correct?

https://photos.app.goo.gl/CYrQHnv3tsZGur888

Also to get fuel pressure can I temporarily drop in an inline gauge in place of the fuel filter or is there a simpler way?

https://photos.app.goo.gl/8tXyemeUvA1wzKtb6

Back To Top PM Quote Reply

 Posted: 12-19-2018 03:28 pm
  PM Quote Reply
9th Post
Frank Schwartz
Member
 

Joined: 02-18-2011
Location:  
Posts: 300
Status: 
Offline
No, no, no...you want to read the fuel pressure, not the oil pressure... and it should be
in the fuel line...Remove the line going to the T to the carbs and put a pressure gauge in that line. Turn the key to "run" and you may or may not hear the pump running, depending on the type...and you then should be able to read the pressure which went to the carbs, but now goes to the gauge. Most any car parts store has them..I think Mr.Gasket has one that is calibrated up to ten pounds. At least that is the way I check it If it is an IN LINE gauge, you can put it right there between that glass filter and the T
Frank

Back To Top PM Quote Reply  

 Posted: 12-19-2018 03:34 pm
  PM Quote Reply
10th Post
Frank Schwartz
Member
 

Joined: 02-18-2011
Location:  
Posts: 300
Status: 
Offline
Ooops...I am "partially" incorrect. I somehow thought you meant the oil pressure. If you have an in line gauge, that is a gauge with an in and out fitting..you will want to put it in between the glass filter and the T and read the pressure. Or if it is a one fitting gauge...just put it in the same place and read the pressure going to the gauge itself. Same thing. Sounds complicated, but is simplicity itself.
Frank

Back To Top PM Quote Reply

 Posted: 12-20-2018 04:35 pm
  PM Quote Reply
11th Post
Tom Bradley
Member
 

Joined: 07-15-2013
Location:  
Posts: 136
Status: 
Offline
It just pulls out to replace the O ring correct?


Unfortunately (and hopefully) not. If it has not been broken, then there are internal hook-shaped plastic prongs that hold the plug in. So to replace the o-ring without breaking the hooks you have to remove the whole carb bottom and push the bottom plug out while pressing the hooks inward. I think the approved method is to use a tube to press the hooks inward. What I have done is to press the hooks inward one at a time with pliers or a screwdriver while slowly working the plug out. This has to be done with with care because when the plugs get old, as yours look to be, the plastic gets brittle and breaks easily. From what I have heard the o-ring will hold the plug in if the hooks are broken off but I would not trust it.

If you do one carb, I would recommend doing both. Even if the front one is not leaking yet the o-ring is probably just as old and will start leaking before long.

Last edited on 12-20-2018 04:38 pm by Tom Bradley

Back To Top PM Quote Reply  

 Posted: 12-20-2018 04:53 pm
  PM Quote Reply
12th Post
JGriff
Member


Joined: 11-21-2018
Location: Boston, Massachusetts USA
Posts: 12
Status: 
Offline
Thanks. I just ordered a rebuild kit. Going to take the plunge and rebuild the carbs.

Back To Top PM Quote Reply

 Posted: 12-20-2018 06:26 pm
  PM Quote Reply
13th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 386
Status: 
Offline
There should be two gaskets in the choke (aka, enrichment device). One internal to the choke itself, and one between the choke and the carb body. Rebuild kits only supply the one that is internal to the choke. The other one needs to be ordered separately.

If the gasket between the choke and body is omitted during assembly, then fuel can leak out there.

Also note that it's easy to assemble the 'choke' incorrectly by installing the choke disc 180 degrees off (flipped over), in which case it may leak fuel. In addition, the choke may either not function, or never shut off. In the former case the engine will be hard to start when cold. In the latter case, the mixture will be excessively rich mixture at all times. This is another possible cause of excess carbon in the exhaust.

A compression spring slips over the Cold Start spindle (along with the special U-shaped circlip that snaps into the groove in the shaft) and forces the moving disk tightly against the fixed mating surface. That forms a sliding 'face seal', much like a water pump seal. Without the spring, the sliding joint could be loose enough to allow for a fuel leak. Even with the spring, if the sliding surfaces are corroded or otherwise rough or nicked, they won’t form a seal.

Regards,
Tim Engel

Last edited on 12-20-2018 06:33 pm by Esprit2

Back To Top PM Quote Reply  

 Posted: 12-20-2018 07:26 pm
  PM Quote Reply
14th Post
JGriff
Member


Joined: 11-21-2018
Location: Boston, Massachusetts USA
Posts: 12
Status: 
Offline
Tim - thanks. I've been looking at some of your documentation in the file section of the JH facebook page. I'm sure I'll be referring to it a lot as I get into things.

Back To Top PM Quote Reply

 Posted: 12-25-2018 06:43 pm
  PM Quote Reply
15th Post
noomg
Member
 

Joined: 08-02-2018
Location: Long Beach, California USA
Posts: 117
Status: 
Offline
JGriff,

I replaced my original pump with a Facet 25 years ago, it still works fine and that's without any kind of regulator in line.

Rebuilding your ZSs first is a good idea, it's a cheap and relatively simple way to go. You can always go Dellorto if you're not happy with the ZSs afterwards.

As far as leaks go, there are two kinds; fuel(important), air(annoying). The rebuild kits are usually general kits and will usually fix the fuel leaks but do little to address air leaks. The most notable symptom of an air leak is a lumpy or uneven idle. This is usually caused by worn throttle shafts and bushings. Easy way to check for air leaks, with the motor warmed and running spray WD-40 on and around the carbs, if there's a leak you'll get an RPM change. Once the carbs are off changing the shafts and bushings is fairly straightforward.

Don't forget your jets and needles, if the jet hole is oval or needle has scrapes or is shinny on one side, replace both. All this is easier than it sounds, the hardest part will probably rounding up the parts.

Back To Top PM Quote Reply  

Current time is 07:59 pm  
> Jensen Healey & Jensen GT Tech > Carburetors > Rebuild or upgrade? Top




UltraBB 1.172 Copyright © 2007-2011 Data 1 Systems