Carbs Running Rich

[glemon]

I have a 54 BN1 with H4 carbs, I have my engine up and running after a rebuild, I did raise compression and go to a M spec cam, I would have guessed if anything I would need to enrichen the mixture with the new specs.

I have the mixture nuts all the way to the top and it is still too rich--when I raise the pistons slightly or even more than slightly it speeds up.

I have checked the choke adjustment and jets they are not stuck open.

I have two theories, carbs are just way worn out (I have not replaced the jets and needles) or my aftermarket fuel pump is pumping too much gas, it seems to be defeating the needles. The pump is supposed to be the low pressure facet, 1.5-4.5 pounds) but it seems to be pumping too much juice. I had grose jets, but put my needles back in, no discernable difference.

I am in the process of getting the old SU pump fixed/replaced--any other thoughts on this issue.

 

[AH100M]

1) Double check the float level.
2) Replace the needles. When they wear they typically cause rich running. You might want to get the standard needles plus one size richer just so you can fiddle more. A crab rebuild without replacing the needles is not a good idea. You HAVE rebuilt the carbs recently, right...?

 

[glemon]

No, have not rebuilt the carbs, when I got the car (7 years ago) asI recall I put new seals on the jets and cleaned them up--I didn't know needles wore out, if installed right they shouldn't get much if any friction I wouldn't think.

But I think too rich at all the way up the adjustment range would be the equivalent of a heck of a lot of wear on the needles, then again the car is 50 plus years old, it most anything could be worn out or replaced with the wrong part.

 

[tahoe healey]

Be sure of the proper placement of the needles. If set to far into the piston they will cause a rich running carb. Have you checked the float adjustment?

 

[glemon]

I have been messing with the float adjustment, the fuel pump seems to be able to overcome the floats closing the needles (both grose jet and standard, I experimented) when I remove the dahpots I get a gusher out of the front carb.

It is non-standard, facet type from NAPA, the low pressure model, but apparently not low enough.

I am going to revive the SU pump and see how that goes.

Thanks, experimenting with the float level helped to idnetify the problem, no matter where set it I got the gusher, I was able to stop it intermittently, but it always came back.

Oh, yes, before anyone asks, the floats are fine, I took them both out, no liquid in them.

Greg

 

[Dave Russell]

Make sure that the float bowl vents are actually working. If not, any fuel going in will be pushed out of the jets.

The H4 bowls can have two types of venting. One type relies on a slot cut across the hold down nut seating area, a cup shaped washer on top of this slot, & an annular area between the hold down nut & the cap to provide float venting. If there is a gasket between the bowl top & the cup washer, or the cup is missing the gasket will obstruct the vent slots.

The second type has a banjo with long overflow tube between the float bowl top & the hold down nut. Again, there is an annular space between the hold down nut & the bowl top.

It requires an internally scalloped fiber washer between bowl top & banjo, a non scalloped washer & metal washer between the banjo top & the bottom of the hold down nut. The vent path is from bowl, through annular area, through gasket scallops, into banjo, & out banjo tube.

I suspect you will have this second type. The key is the scalloped washer.
D

 

[glemon]

Thanks Dave, that makes sense I have looked at these and will make sure I get the vent correct.

Greg

 

[glemon]

Thanks Dave, I have one carb with the banjo and drain tube and one without, the one without was not venting, hence not allowing float to rise quickly and shut off the gas, as you suggested, it did not appear that there was a good way to vent it with the top nut (float bowl cap retaining nut) I had.

I modified the nut with two cuts of a hacksaw as shown below, problem appears to be solved, but wifey is sleeping and the bedroom is over the garage (design flaw, next time I will know better) so final running and adjustments will have to wait unitil tommorrow.

How long the car has been that way it anybodies guess, since I got it 8 years ago and before I guess. It always seemed to run rich, but the new fuel pump made the problem worse. Wondered why my MPG was so bad, glad it was figured out before too much raw gas was dumped in the cylinders/pistons.

 

[Dave Russell]

Not only would the non vented bowl not allow the float to rise, the pressure build up would force any fuel out the bottom of the bowl & directly into the jet.

If the non banjo vent is intended, there is a slot cut across the aluminum cover hold down boss, slot about .040" deep & .080" wide. It should have a somewhat oversize metal cup washer with a side cut out, over this slot & under the bolt head.

Wouldn't hurt to check the other carb to see if everything is really correct.

I really prefer the banjo type vent, no carb slot. To do this, you would need another longer hold down nut, banjo, scalloped washer, & regular washers.

The assembly is somewhat complicated by the bowl steady brackets that also mount under the bowl cover bolts. The manifold end of the brackets can be loosened to make the fit easier. If these brackets are missing, they really should be added. Item #27here: https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28851
D

 

[glemon]

Not only would the non vented bowl not allow the float to rise, the pressure build up would force any fuel out the bottom of the bowl & directly into the jet.

Yes, I got that phenomenon, it was in fact gushing out of the jet when I pulled the dashpot and piston, this is how I first figured there was some float bowl problem

If the non banjo vent is intended, there is a slot cut across the aluminum cover hold down boss, slot about .040" deep & .080" wide. It should have a somewhat oversize metal cup washer with a side cut out, over this slot & under the bolt head.

Missing cup washer, thought of trying to make something that, suppose I could make one, but the pictured mod seems to be working

Wouldn't hurt to check the other carb to see if everything is really correct. I have an oversized washer on this one, similar to the scallopped item, allows the air to vent

I really prefer the banjo type vent, no carb slot. To do this, you would need another longer hold down nut, banjo, scalloped washer, & regular washers. I am guessing my car had two banjo types at one time, but one got lost, assume they usually matched when new

The assembly is somewhat complicated by the bowl steady brackets that also mount under the bowl cover bolts. The manifold end of the brackets can be loosened to make the fit easier. If these brackets are missing, they really should be added.

I do have these brackets, great info, thanks again

Item #27here: https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28851
D

 

[glemon]

Argghhh! I think I did solve some issues with the float vent, but it still is rich beyond adjustment, having exhausted all remdies I guess it is time to spend (more) money.

Greg

 

[Patrick67BJ8]

Argghhh! I think I did solve some issues with the float vent, but it still is rich beyond adjustment, having exhausted all remdies I guess it is time to spend (more) money.

Greg

For thought...I received a rebuild kit that had different sized needles(too small diameter) than the actual jet holes. This was for a BJ8, but maybe in can happen to other series cars too?
Patrick

 

[Patrick67BJ8]

I have been messing with the float adjustment, the fuel pump seems to be able to overcome the floats closing the needles (both grose jet and standard, I experimented) when I remove the dahpots I get a gusher out of the front carb.

It is non-standard, facet type from NAPA, the low pressure model, but apparently not low enough.

I am going to revive the SU pump and see how that goes.

Thanks, experimenting with the float level helped to idnetify the problem, no matter where set it I got the gusher, I was able to stop it intermittently, but it always came back.

Oh, yes, before anyone asks, the floats are fine, I took them both out, no liquid in them.

Greg

Greg,
How did you get it to stop intermittently??
Patrick

 

[glemon]

It stopped a couple of times when iwas messing with float adjustment, but came back after started and stopped a coupe of times.

 

[Patrick67BJ8]

It stopped a couple of times when iwas messing with float adjustment, but came back after started and stopped a coupe of times.

I never got a gusher from a float bowl adjustment, but I did when I had problems with the jet's. Do you get gas coming out of the overflows?

 

[glemon]

I was not getting gas out of the overflows because I essentially didn't have one on the front carb, since it had nowhere to go, and the gas flow pressurized the air in the float chamber instead of just filling it, hence no raised float so the gas kept coming and the fuel gushed out of the jets because it had nowhere else to go.

As far as the kit and mismatched jets and needles who knows?, my car led an interesting life prior to my ownership, could have a mishmash of parts here and there.

I am going to order new jets and needles--then go through the fun process of reassembling carefully to make sure no leaks on the jet--and see if that helps the rich running problem, the fuel gusher appears to be solved

 

[Dave Russell]

For thought...I received a rebuild kit that had different sized needles(too small diameter) than the actual jet holes. This was for a BJ8, but maybe in can happen to other series cars too?
Patrick

Greg's carbs are SU H4's.
H4's have .090" dia. needles
The next size up is H6 which uses .100" needles
H8's, HD8's on BJ8's use .125" needles

Since H4's use the smallest needle, it would not be possible to get too small needles in his carbs.

Greg,
Possibilities for too rich:
!- The float levels are not set correctly, 7/16" bar between the inverted carb lid & the forked lever (no compression on the spring loaded needle pin if it has such) & the float bowl.

With the ball type inlet valve it's sometimes hard to get the correct float level set. The spring plunger neoprene tipped float needles work well & usually come out at the correct setting.

2- The float hinge & float needle are binding.

3- The inlet seat is not fully tight in the lid.

4- The bowl is not properly vented & the bowl is pressurized.

5- Fuel pressure too high

6- Wrong jet - should be exactly .090" ID

7- Wrong needle - should be type QW

8- Fuel leakage AROUND the jet. Fuel enters the jet through a hole in the side of the jet & exits at the top between the needle & jet. In the spring area, #5 below.

There are cup washers & cork rings at the top & bottom of the jet & a spring between them. If the seals leak, fuel will bypass the jet/needle assembly.

The jet assembly & seals from top to bottom would be:
1- Copper washer for upper jet bearing
2- Upper jet bearing
3- Upper cork seal
4- Upper gland washer with dished side toward cork (up)
5- Gland spring
6- Lowerer gland washer with dished side toward cork (down)
7- Lower cork seal
8- Lower jet bearing
9- Brass washer for lower jet bearing
10- Jet locking nut cork seal washer
11- Aluminum sealing ring, dish toward cork
11- Jet locking nut
12- Spring for jet nut
13- Jet adjusting nut
14- Jet head

With the jet adjusting nut set fully up, the top of the jet should be nearly flush with the jet bridge in the carb.

At this point I would double check all items. With the carbs unknown history anything is possible.
D
PS - If the carbs have been sitting dry for a long time, it's possible that the jet cork seals have dried & lost their seal. It's usually suggested to soak the corks in oil overnight to make them pliable for a good seal.

 

[Patrick67BJ8]

For thought...I received a rebuild kit that had different sized needles(too small diameter) than the actual jet holes. This was for a BJ8, but maybe in can happen to other series cars too?
Patrick

Greg's carbs are SU H4's.
H4's have .090" dia. needles
The next size up is H6 which uses .100" needles
H8's, HD8's on BJ8's use .125" needles

Since H4's use the smallest needle, it would not be possible to get too small needles in his carbs.

Greg,
Possibilities for too rich:
!- The float levels are not set correctly, 7/16" bar between the inverted carb lid & the forked lever (no compression on the spring loaded needle pin if it has such) & the float bowl.

With the ball type inlet valve it's sometimes hard to get the correct float level set. The spring plunger neoprene tipped float needles work well & usually come out at the correct setting.

2- The float hinge & float needle are binding.

3- The inlet seat is not fully tight in the lid.

4- The bowl is not properly vented & the bowl is pressurized.

5- Fuel pressure too high

6- Wrong jet - should be exactly .090" ID

7- Wrong needle - should be type QW

8- Fuel leakage AROUND the jet. Fuel enters the jet through a hole in the side of the jet & exits at the top between the needle & jet. In the spring area, #5 below.

There are cup washers & cork rings at the top & bottom of the jet & a spring between them. If the seals leak, fuel will bypass the jet/needle assembly.

The jet assembly & seals from top to bottom would be:
1- Copper washer for upper jet bearing
2- Upper jet bearing
3- Upper cork seal
4- Upper gland washer with dished side toward cork (up)
5- Gland spring
6- Lowerer gland washer with dished side toward cork (down)
7- Lower cork seal
8- Lower jet bearing
9- Brass washer for lower jet bearing
10- Jet locking nut cork seal washer
11- Aluminum sealing ring, dish toward cork
11- Jet locking nut
12- Spring for jet nut
13- Jet adjusting nut
14- Jet head

With the jet adjusting nut set fully up, the top of the jet should be nearly flush with the jet bridge in the carb.

At this point I would double check all items. With the carbs unknown history anything is possible.
D
PS - If the carbs have been sitting dry for a long time, it's possible that the jet cork seals have dried & lost their seal. It's usually suggested to soak the corks in oil overnight to make them pliable for a good seal.

I have BJ8 with HD8's and I would assume that since the needles were considerably smaller than the jet holes, that I was sold a mismatched repair kit. One thing about the SU carbs that I have learned is that 95% of the time you can make a quick roadside fix and no problems. The other 5% is why the poor owner is really having problems. Sometimes it's worth the money to have the carbs "restored" by someone that knows them backwards and forwards.
Patrick

 

[Dave Russell]

I have BJ8 with HD8's and I would assume that since the needles were considerably smaller than the jet holes, that I was sold a mismatched repair kit. One thing about the SU carbs that I have learned is that 95% of the time you can make a quick roadside fix and no problems. The other 5% is why the poor owner is really having problems. Sometimes it's worth the money to have the carbs "restored" by someone that knows them backwards and forwards.
Patrick

Exactly - Since the HD8 carbs on the BJ8 use .125" dia. needles, the .090" or .100" needles from H4 or H6 carbs would go into the the larger jet & be extremely rich. But not the other way around. If you want to know more about the carbs, there are a couple of good SU carb manuals available. The fattest step on most all SU needles is only about .002" smaller than the jet.
D

 

[healeynut]

Patrick -

It's really common with hack mechanics to switch needles in an SU carb and then forget about it. When I got my '52 Atlantic (same motor as the 100), the car ran like crap.

After fiddling with it for a couple hours we popped the dashpots - sure enough one needle was way too short and the other was out of an MGB.

Luckily I had two old OEM A90 needles sitting in my basket, put them in, car ran like new.

Cheers!