The Stovebolt Site Forums The Shop Area Engine Shop Fuel Pump Too Much Pressure

Has anyone ever had a mechanical fuel pump suddenly start giving too much fuel pressure causing the engine to flood? If so, how do I test to see if it is putting out too much pressure? The carburetor seems to be fine. Not warped. Needle and seat work properly. It is flooding when I try to start it to the point that it will not start. I'm getting a pool of gas sitting the bottom of my air intake. I'm getting spark at the plugs and my initial timing is set right. I am just wondering if the NAPA fuel pump I put on last year could suddenly have failed and started putting out too much pressure.

Have you checked your float level? That sounds like a float problem.

I have seen some issues (and read about a lot more) of floats getting holes or being porous and sinking.

Flip side is: throw a fuel pressure gauge on and see what you have. Autozone will lend you one for free.

A fuel pressure/vacuum gauge costs less than $20.00- - - - -a lot less if you buy one on Ebay. I can't imagine any shop that doesn't have one!
Jerry

About a year ago I changed my fuel pump. I had 3 brand new pumps to choose from on hand and I was struck by how wildly different they all were in pumping pressure. I did not measure output, just worked the arm manually and it felt like they varied from 10lbs of required pressure to 40lbs.

There really isn't a way that a fuel pump would suddenly put out more pressure. That is unless it had a sticky check valve that suddenly freed up, but that's pretty unlikely.
I'd second the suggestion that it's a float problem rather than a fuel pump problem.

Yes, a mechanical fuel pump can change pressure as it ages. As the diaphragm gets older it can become stiff. This in turn causes higher pressure to be generated. I was having the same issue with a VW Beetle. The Beetle was having flooding problems, and the pressure was 4.6 psi when I checked it. A pressure of around 2.6 psi was the recommended pressure. After checking a few sites, I came across an article that gave that as a reason. I installed an after-market regulator and brought the pressure to 2.6 psi and the problem was solved.

Thinking on this I am thinking that ethanol in the fuel may be a contributing factor to the diaphragm becoming stiffer. Just my thought on it.

The only ethanol -related problem I have ever experienced is when it killed the original pump in my '56 Cadillac. It softened the original diaphragm causing it to expand.. This resulted in the volume of fuel pumped to be reduced by 1/2.

New, off the shelf pumps are absolute junk, however, pressure test your system to make sure your pump is actually the culprit.

Once you rule the pump out (or in) you can start looking at the carburetor.

Just about everything posted here is why I have since 1997 used an electric fuel pump...a cheap one, in fact. I use the Autobest F4027 which puts out about 3~3.5 psi and costs about $30 on Amazon. Ethanol does not bother it a bit. Just remember, electric pumps are designed to push, not pull. Mount it back where the tank is, in the frame recess and out of harm's way.

Yes...if the pump diaphragm on the old VW bug got stiff (and they did, especially in summer heat and very especially in a place like Dallas where an air cooled engine was always behind the 8 ball), the pressure would increase and you'd have flooding problems until you bought a new pump or a new diaphragm if you could find one by itself. The tip-off was your gas mileage would start declining and your muffler would belch black smoke all the time. I don't think I ever got more than 2 years out of a VW fuel pump.

3 psi is all you need for the 235 six and you will do just fine at 2.5 psi. Anything above 4 psi isn't good. The Chinese made mechanical pumps are horrible.

I’ve got the fuel psi set at 3.5 on my 454 with 750 Edelbrock carb & electric fuel pump with 3/8 fuel line. We only need enough pressure to keep the fuel bowl full

I have submerged the float in water and no bubbles. Someone suggested making the water hot (just pre-boiling). I did not do that though. The water was cold that I submerged it in.

Generally speaking...a couple of things: water doesn't have to be hot. That helps if your float has smaller holes. Two: if your float is leaking it will have gas (and/or water) in it. Shake it back and forth and see if you hear anything. Please help me catch back up. At one time you had a Rochester carburetor and at another time I think you may have mentioned getting a Carter carburetor. Which do you have at this point?

A bent float can hit the side of the carb delaying or preventing it from closing the needle, causing flooding all of the time or some of the time.

I’ve still got the Rochester. I bought a Carter 2100 from a guy on marketplace but should have asked about the space between the mounting holes. The Carter I bought is spaced for 2 11/16” air intake mounting bolts. The one I have one the truck is for 2 15/16”. I do have an extra intake that will work with the Carter. I will just have to swap out the intakes and order an insulator.

Most Carter YFs have a slotted throttle base that fits both stud spacings. You still need a carb that's jetted and calibrated for approximately the right size engine. The correct venturi size is very important.
Jerry

Here is what I got.

Carbking will be able to let you know if you can rebuild that one to work on your truck or whether you got a pig in a poke.

The carb you bought (YF 2100s) SHOULD have the larger, 2-15/16 base. That one got swapped at some point in its life to the smaller size.

All is not lost. It shouldn’t be impossible to find a donor or stand alone throttle body in the correct size/casting number. Let me look through my photos and see if I can find the number you’d be looking for.

Thanks!

I believe 1-788 is the correct CASTING number throttle body for a 2100s. But it appears to me that same casting was used with different throttle linkage setups on different Carter models. Must be a stamp or some other identifier that differentiates throttle bodies.

I’d better just shut up and wait for Carbking to weigh in.

Nathan, From the pics Matt posted, it shows he purchased a YF2100 - not the YF2100S. IIRC, the YF2100 was sized for the 216 and YF2100S is sized for the 235. You are correct that the YF2100S shoud have the "1-788" casting number on the throttle body. Jon "carbking" and others will probably chime in here to clarify the info.

Matt, Jerry "Hotrod Lincoln" is right on the money that the smaller 216 rated carb isn't what you need for the 235, even if you change the throttle body to the larger size. You need to locate a "YF2100S" like this one. That linked "carb" is just a sample I found on line in a short search. There are others out there if you search more.

The 2100, whether you use the “S” on the end or not….is a 235 carb. Most/all of the stampings I have seen have the S, sometimes very faint. But I’m 99% certain a 2100 is the same thing with or without the S.

See the tech tips section in this forum for Carbkin’s complete listing of Chevrolet-application YF carbs. You will not see 2100 listed for a 216.

Edit: Upon further review, the listing of Chevy carbs in the tech tips doesn’t list the 2100 at all. Only the 2101, which is the auto choke cousin of the 235.

However….see the attached document for 2100(s) application.

Nathan, I see your point and have no personal knowledge of the carb Matt pictured that shows a "YF2100" (no S) stamping being specifically for a 216. Just what I recall reading at some point or another. I very well could be wrong and hope "carbking" can clear this up as you mentioned. Everything I have researched/read though, indicates that the throttle body for a "235" Carter YF should be the one with casting# 1-788. The throttle body on Matt's carb has casting# 1-630, which I believe (again I could be wrong) is for 216 applications (YF 756S, 787S, 964S, 965S and 2008S according to "carbking's" Carter YF for Chevrolet list.

Will wait for others to chime in to help Matt resolve his dilemma.

Probably just me but I don't recall any of the YF models not being followed by S. Maybe there were, but the data I have doesn't show it. The number stamping on this one is so faint toward the right side it may simply be the S just isn't visible...I can almost not see the last 0 there. The throttle body casting number is generally associated with the 216 carburetors, but Jon H (carbking) has said in the past those numbers apply to casting dates, etc and the measurement is the most important thing. Still, that is a throttle body for a 216. I've seen lots of them.

The 2100s is popular and in my opinion might be overpriced these days. I might blame the interesting (and to me unusual) allure of a manual choke, but almost all the YF models have shot up in price also. The popularity/scarcity has caused some people to swap parts and the throttle body is a common swap to "make" a 2100S that can be sold. I bought a 2100S a few years ago from a gentleman here which had been dropped and as a result of which the throttle body had been broken. In fact I just discarded that broken throttle body as I couldn't figure out how to fix it suitably. Today parts carburetors are hard to find. But the right throttle body is what is needed here. I have one but it would have to be repaired as the linkage side of it has been damaged and removed. Let's see if anyone else offers anything...

So I did some searching through Stovebolt and found this reply post to a thread Nathan (JW51) started about an incorrect throttle body on a YF2100S.

Per Jon H's (carbking) reply, the YF2100S should have a throttle body stamped on the base mounting face that reads "1127". I currently have a YF2100S and (big sigh) confirmed the throttle body on it is an "1127" - whew!!! He also mentioned that a YF2101S throttle body should be stamped "1121". More on this below.

A little further searching and I came across this post by "carbking" that provided the following details on 216 and 235/261 carbs:


While looking at my YF2100S, I remembered I had another YF Franken-carb that was in a box of spare parts I got with the truck. It turned out to be a hodge-podge of parts to make up the thing. Of interest is the fact I have a YF2101S throttle body - stamped "1121" on the mounting flange and showing casting# 1-788 that is temporarily homeless.

If this particular throttle body for a YF2101S will work on a YF2100S bowl assembly, I think it could find it's way to Matt. Just need to get confirmation that this throttle body will work for the YF2100S???

Just a follow up to my last reply that after relooking at the YF 2101S throttle body I have. It appears that the throttle linkage arm is unique to the YF 2101S and isn't usable on the YF 2100S. There is no mechanism/arm connection to the manual choke plate rod assembly to the upper section of the carb. Sorry it seems it won't work out.

Are these the linkage pieces we're looking for, Dan?

Looking at the linkage rod I think the one for the 2100S is longer and different. I know about 5 or so years ago I had to borrow one from Jerry and copy it for a carburetor I had here. Wish I had made 2 of them.

PastorMatt - At very best that YF is a "Frankencarb" (I really think from the pictures it is a fake, but would have to see it to be sure). In any event DON'T USE IT!

A few comments, with absolutely no offense meant to anyone:

(A) I do not remember ANY Carter YF carbs with a factory slotted throttle body, they are either drilled for 2 11/16 or 2 15/16 inch centers. Some of the universal Carter type WA-1 did come with a slotted TB.
(B) Below is copied from my website:

Carter numbering systems. Three different types of numbering systems are found on Carter produced carburetors.

(1) On carburetors built for Chrysler Corporation, a series of 3, 4, or 5 letters and numbers; i.e. EV1 or D6H2.

(2) On carburetors built for Ford Motor Company, the “Ford” numbering system which is “lnll – l(l)(l)” or letter, number, letter, letter dash letter (possible letter) (possible letter) i.e C5VF-A. This system is codified in that the first letter is the decade (B=1950’s, C=1960’s, etc.); the number is the last digit in the year; the 3rd and 4th letters (before the dash) represent the vehicle model (VF=Lincoln); and the letter or letters after the dash are a modifier which distinguishes the exact application. Thus in the example C5VF-A, the carburetor would have been the first application for Lincoln in the year 1965.

(3) The traditional Carter numbering system which consisted of 1, 2, 3, or 4 digits; followed by the letter “S”, possibly followed by another letter. It is extremely doubtful that any of the single, double, or early triple digit tags will appear; as they were produced before 1930 and were constructed of red cardboard. The metal tag appeared about 1930 with tag numbers of about 300s. The 4 digit tag appeared in 1952, and was continued on until the end. The letter S and following letters, when present, have caused much speculation (mostly incorrect). In Carter’s terminology, an individual part such as an idle mixture screw was a single part; whereas two or more individual parts sold together such as a needle, seat, and gasket were sold as an “assembly”. Carter used the suffix letter S to denote assembly. Since all carburetors are composed of multiple parts, the letter S was appended to all carburetors using the traditional numbering system i.e. 938s. If a significant engineering change was made to the carburetor, the letter “A” would be appended to the S (i.e. 938sa). A second change would have the letter A replaced by the letter B (i.,e. 938sb). The highest engineering change of which I am aware is 4 i.e.938sd. Contrary to popular belief, the S DID NOT mean standard transmission, nor the SA automatic transmission.

(C) ALL genuine 2100s carbs will have the "s" stamped after the 2100.
(D) As mentioned by others, the pictured throttle body is from a 216 YF.
(E) SPECULATION: Some of the earliest YF's did not have an identification number stamped, anywhere. Why, I don't know. Possibly sold through J.C. Whitney??? Other early YF carbs had the ID number stamped where yours is stamped. So where yours IS stamped IS a valid location. Your bowl appears to be one of the early bowls. 235 carburetors are MUCH more valuable than early unstamped 216 carburetors. Metal stamping sets are readily available.

EDIT: The 2101s has "1121" stamped on the face of the flange; the 2100s has "1127" stamped on the face of the flange. The throttle arms, and linkage are different.

Jon

Would I be able to use the plate and rod off the one I have and put it on the throttle body you have?

Does anybody know where I can buy a Carter YF2100s already rebuilt? Looks like they are expensive even ones in really poor condition.

Yes, I think that would be an excellent scheme. One already rebuilt will be difficult to obtain but we can help get yours fixed or you could send it to me and I'll gladly do it for you.

To Carbking’s concern about the possible 2100s forgery…..

Could Matt measure the venturi and validate whether he has a fake or just a Franken-carb?

(I don’t know off the top of my head if there was a venturi size difference between 216 and 235 carbs)

Perhaps he could check the metering rod against specs, as well.

Matt, I think it may be possible to swap your throttle rod and mechanism from your body to the one I have, but you'd have to use the throttle plate that exists in the 1-788 piece I have. What I don't know, and perhaps Jon H (carbking) can confirm or not, is if the throttle plate mounting holes on the 2 shafts are spaced the same??? Yes the throttle plate screws are staked, but Jon (carbking) or Jon G can explain how to properly remove and replace those. Jon G did say he could help with the conversion if we send him what we have.

On your question of where to buy a YF2100S already rebuilt, there are a few vendors/suppliers that seem to be offering them on the web. Some just offer a rebuild service for your core, which doesn't help with the mismatched parts. The possibility that what ever a rebuilder has to sell may be a franken-carb is pretty high too. Just the nature of the beast. Just my $.02 worth, but find one that you can confirm has all the correct parts and ID numbers (something like the one I linked to in eBay above) and either get a correct rebuild kit from "carbking" to rebuild it yourself or send it to a trusted rebuilder.

Of the rebuilding services and sellers of rebuilt carburetors out there, sadly I can't suggest using any of them. That entire game has changed too much now.

I'm going to be busy with some personal stuff and a couple of other commitments for a couple of weeks but I'll be happy to help sort this out as time allows. Between Dan, you and me I am certain we can solve this.

The problem with swapping carburetor components such as main bodies and throttle housings will be making sure the drilled passages and the gaskets between then align properly. You might end up ruining both carbs if you try a swap. It would probably be a better choice to slot the holes in the existing throttle body. That will allow the carb to be installed on manifolds with either stud spacing. There's still the possibility that the internal calibration will not be correct for your engine. I've seen YF carbs that come from the factory with a slotted throttle body housing. Use SAE type flat washers to cover the top of the slotted housing to make sure the nuts secure the carb to the manifold properly.
Jerry

Plate holes are about 11/16” center to center and the shaft is 3 5/8”. Don’t know if that helps.

If you want to send me your throttle housing, I'll be glad to slot the holes for you with an end mill. I have a milling attachment for my lathe.
Jerry

Matt: it seems like you are running down the parts replacement path pretty fast.

Did you test your fuel pressure? All of this carb work will be pointless if you do have too high of fuel pressure.