TR4/4A Wish I Could Give Up--My Carbs Still HS6 TR4A

KVH · Sep 18, 2016

Addressing my rich running problem, I bought new needles and seats, and new floats, all to no avail. I reset the float levels at least 10 times until the fuel level is just below the bridge per Moss' recommendations. Still skipping and missing on take off and fast acceleration. I then tried "lean" needles, and still no luck. I've adjusted the mixture another dozen times. Nothing stops one of two problems: Either rich and black smoke, or skipping on take off and fast acceleration.

A part of me wants to park it at a local shop. Before I do that I'm going to replace the pump even though it registered about 1.5 psi. About the floats, however, is there any reason that I should disregard all advice and just try setting them way low by increasing the gap from 1/8 or 3/16 to more like 5/16 to 3/8? Do things really get that touchy and technical? Finally, is a missing engine at take off just as likely due to lean carbs as rich carbs?

TR3driver · Sep 18, 2016

You're setting mixture at idle, right? And you've tried heavier oil in the dashpots? The black smoke is at idle, right?

What about replacing the jets? Worn jets are certainly a problem with H6 carbs, and that's just the problem you get : too rich at idle, too lean the rest of the time. I don't have much experience with HS6, but don't see why they couldn't have the same problem.

At least in my experience, even mixture rich enough to cause a miss at idle (eg choke left on too long) will usually clean up and run when you try to accelerate from a stop. It's certainly possible to have a plug so badly carbon fouled that it won't run at all, but I usually only see that when trying to get an engine started.

TFB · Sep 18, 2016

KVH said:
Addressing my rich running problem, I bought new needles and seats, and new floats, all to no avail. I reset the float levels at least 10 times until the fuel level is just below the bridge per Moss' recommendations. Still skipping and missing on take off and fast acceleration. I then tried "lean" needles, and still no luck. I've adjusted the mixture another dozen times. Nothing stops one of two problems: Either rich and black smoke, or skipping on take off and fast acceleration.

A part of me wants to park it at a local shop. Before I do that I'm going to replace the pump even though it registered about 1.5 psi. About the floats, however, is there any reason that I should disregard all advice and just try setting them way low by increasing the gap from 1/8 or 3/16 to more like 5/16 to 3/8? Do things really get that touchy and technical? Finally, is a missing engine at take off just as likely due to lean carbs as rich carbs?

I am not familiar with the Moss instructions but I believe its the same with my h6 carbs.The float level heights are set to get the proper fuel level which is slightly below the main jet end.No guessing required,just look down at the jet after a few engine cranks with the key off.
Tom

KVH · Sep 19, 2016

TR3driver said:
You're setting mixture at idle, right? And you've tried heavier oil in the dashpots? The black smoke is at idle, right? I've been using Moss Motors Dashpot Oil. I'm not sure the weight. The "missing" and poor performance is as follows: On take off from stop. On hard acceleration. When going uphill. Listening and watching, someone might think the car runs great. But I can feel the choking, the skipping etc. Not terrible. Just as indicated.

What about replacing the jets? Worn jets are certainly a problem with H6 carbs, and that's just the problem you get : too rich at idle, too lean the rest of the time. I don't have much experience with HS6, but don't see why they couldn't have the same problem. I have new jets I can install, but this just sort of suddenly started after I rebuilt the engine.

At least in my experience, even mixture rich enough to cause a miss at idle (eg choke left on too long) will usually clean up and run when you try to accelerate from a stop. It's certainly possible to have a plug so badly carbon fouled that it won't run at all, but I usually only see that when trying to get an engine started.

Also, Randall, a few things to add to the confusion. I put my spare fuel pump on, and after a drive this evening (with the same choppy performance, mainly on take-off) I checked my carbs. They were fire hot, and as I was removing one of the piston chambers to check the level at the jet, I could hear two loud puffs of air escaping from somewhere. I've not heard that before. Also, the fuel level in the jets was was low. Usually they were flooding. So, it appears something changed. At a minimum, I need to reset the floats again and see what happens. I guess if nothing works, I'll put in the new jets but something tells me it's not the jets.

TR3driver · Sep 19, 2016

KVH said:
this just sort of suddenly started after I rebuilt the engine.

Ok, have you double-checked the valve timing? Off by a tooth will definitely play hob with the mixture.

I checked my carbs. They were fire hot,

Could they be getting hot enough to boil the fuel in the jets?

I guess if nothing works, I'll put in the new jets but something tells me it's not the jets.

You're probably right, just a long shot. Since it started right after putting the engine together, I now think the valve timing is more likely.

Brinkerhoff · Sep 19, 2016

When you have the valve cover off to check the valve timing , you'll need to roll the engine over enough to make sure the valves have enough lash to close properly when the engine is warm. Then do a quick check of the timing by rolling the engine over with the hand crank and the spark plugs out . The intake valves should start to open ( and the exhaust valves just start to close) just before TDC on the intake stroke.

KVH · Sep 21, 2016

Here's the latest. Ordered yet another new set of Moss floats. Set them perfectly. Cleaned the float bowls, needles and seats. New needles and seats--viton tipped. I'm running rich again, and there's gas on the carb bridges and seeping from the top of the jets. In other words, I'm just proving time and again that there's no solution, and that I'm repeating a process expecting different results, but getting the same. But I now notice something that might be relevant. The "unadjustable" floats I removed from my carbs 4 months ago are bigger than the new ones from Moss that have the metal tang that can be bent for adjustment. Just a rough estimate, I'd say the displacement difference between the float styles could be about 10 percent. Have I stumbled upon anything relevant here?

TR3driver · Sep 21, 2016

Hmm, guess I missed the part about fuel seeping from the tops of the jets. That certainly indicates a float valve problem, not any of the other things suggested.

And having a float that is too small could certainly cause a problem. They have to float with enough force to hold the valve closed against the fuel pressure; a too-small float will just sink instead.

But it could also be that the originals were heavier and hence needed to be larger. So worth looking into IMO, but not necessarily the problem. Sorry, I realize that's not much help.

Brinkerhoff · Sep 21, 2016

Yes , a new development but there is always a solution. Try setting the new floats lower.

KVH · Sep 22, 2016

Brinkerhoff said:
Yes , a new development but there is always a solution. Try setting the new floats lower.

I'm so frustrated.

I lowered the brand new floats and, when I check after a stop, I see gas is still pouring over the bridges and seeping at the top of the jets. If I take the lids off the floats and adjust down further (i.e., a bigger gap), that will easily be the 15th time I've made an adjustment to no avail.

The bowls are clean. My pump is perfect. Either the new floats are no good, or there's something extremely elusive going on here. My needles and seats are also new, and Viton tipped.

When I shut down the engine, I always "clutch it" to avoid pre-ignition. Would that force fuel to the top of the jets? What about the prior owner putting in slightly "lowered" springs? I'm about 1.5 inches lower than normal.

The spec for the float gap is 1/8 to 3/16ths of an inch. My current gap is 1/4 inch, with the fuel still spilling at the jets as indicated. Is this one of those things where the answer is really simple and staring at me in the face? (other than take it to a shop).

P.S. If I put the old floats back in, the gap is barely 1/8 of an inch, but I can try to find very thin fiber washers and start that exercise. I would have already except that every fiber washer I've found expands the gap unacceptably--to 1/4 inch or more.

TR3driver · Sep 22, 2016

So, what happens if you try the old floats with the 1/4" gap?

Killing it with the clutch, and lowered suspension, should have no effect on float level.

FWIW, I pulled a HS6 carb from the parts bin (probably off a Volvo), and the float height was closer to 1/4" than 3/16".

Looks like it would take about .018" to lower the float level by 1/16". I don't have one handy to measure, but I'd guess that a Coke can should be close to that. And the soft aluminum should deform enough to make a good seal.

TFB · Sep 22, 2016

KVH said:
I'm so frustrated.

I lowered the brand new floats and, when I check after a stop, I see gas is still pouring over the bridges and seeping at the top of the jets. If I take the lids off the floats and adjust down further (i.e., a bigger gap), that will easily be the 15th time I've made an adjustment to no avail.

The bowls are clean. My pump is perfect. Either the new floats are no good, or there's something extremely elusive going on here. My needles and seats are also new, and Viton tipped.

When I shut down the engine, I always "clutch it" to avoid pre-ignition. Would that force fuel to the top of the jets? What about the prior owner putting in slightly "lowered" springs? I'm about 1.5 inches lower than normal.

The spec for the float gap is 1/8 to 3/16ths of an inch. My current gap is 1/4 inch, with the fuel still spilling at the jets as indicated. Is this one of those things where the answer is really simple and staring at me in the face? (other than take it to a shop).

P.S. If I put the old floats back in, the gap is barely 1/8 of an inch, but I can try to find very thin fiber washers and start that exercise. I would have already except that every fiber washer I've found expands the gap unacceptably--to 1/4 inch or more.

Must be frustrating but I believe you are still working on the same problem,maintaing proper fluel level.No need to even start the motor until this is resolved.
Try removing float top and check the float for free movement ,then flip over and with a tube on the fuel inlet see if it will pass the suck test.Then adjust according to jet level.If level changes after cranking or turning on pump if electric then the valve is leaking by or the inlet pressure is to high or the floats are heavier or smaller than original which will require a lower setting.
Putting floats in a clear jar of gas can also be revealing.
Good Luck
Tom

KVH · Sep 22, 2016

OK, I'm on it. Wait--what is the suck test? Sucking back to see if the viton needle really is sealing?

Brinkerhoff · Sep 22, 2016

I still think it sounds like the little flaps on the float lids are plugged so the lids are not venting. Its critical that the top of the lid is vented either with the overflow drain tube or the little aluminum flap on the top of the lid . If the float lids don't vent the float bowls will have an air pocket trapped so that the float will not rise and shut off fuel. The fuel will spill over the jet bridge.

KVH · Sep 23, 2016

I lowered the floats last night, and when checking the jets found that gasoline is still sitting right at the bridge, at the top of the jets. The car ran really great, but I felt some hiccups on acceleration from a stop, and I'm certain it's the same problem. I'm now going to try Randall's suggestion of putting my old floats back in and letting the gap increase to 1/4". Frankly, even with the smallest washers I can find, the gap will be more like 5/16".

I'm going to keep working on this, trying different things, and posting my results and findings right here, at least until they come to take me away.

TFB · Sep 23, 2016

KVH said:
OK, I'm on it. Wait--what is the suck test? Sucking back to see if the viton needle really is sealing?

Yes thats the idea.Apply a small vacuum ,sucking on a tube is easiest,to see if the valve assembly seals.
tom

titanic · Sep 23, 2016

Just a thought, but make sure the float bowls are level. SU HS carbs have adapters to match the angle of the float chambers to the manifold, so that the float bowls are level, regardless of the manifold angle. Some people just cut the tabs off the adapters and move the float bowl until it is level. Anyway, if the float chamber isn't level, it may cause flooding.
Also, I believe that the std. metering needle should be TW with a .100" jet. The VB catalog shows a QW needle, which is used with a .090" jet and would provide a grossly rich mixture if used with a .100" jet. The Haynes SU manual shows 2 listings for SU HS6 carbs used on the TR4A. One with a TW needle with .100" jet and separate listing for 1968 USA cars with a QW needle and .090" jet. Very confusing and I wonder if it is an error. Maybe someone else has an explanation.
Berry

KVH · Sep 24, 2016

titanic said:
Just a thought, but make sure the float bowls are level.
Berry

No way my float bowls are level. I figured that was part of the design. Any more info on adapters?

TR3driver · Sep 25, 2016

Over on the side of the carb away from the float bowl, partially hidden by the choke linkage to the jet, is a bolt with no apparent purpose. If you unscrew that bolt, you can pull the float chamber off the side. The adapter is between the bowl & body (probably will come off with the bowl where you can pull it off with your fingers).

Looks like TRF has the adapters available new, 515241 and SUAUD2072 Or, as Berry said, position the bowl, tighten the bolt and friction should hold it in place.

charleyf · Sep 25, 2016

My Haynes SU OWNERS WORHSHOP MANUAL lists the 209 carbs with the SW rich, TW standard and CIW weak. The 284 carbs QW standard and no rich or weak needle. These are all listed under the .100 needles. I really like the 209 carbs and have converted my two TR4s to use them.
When I get the full rebuild kits for these carbs I usually get the appropriate float bowl adapters for the 209's in the kit.
Charley

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TR4/4A Wish I Could Give Up--My Carbs Still HS6 TR4A

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