Mid Range RPM Hesitation

[Zedyone_kenobi]

Hey guys I have the same issue as landmizzle for a while. In fact we should compare notes mizzle!

I put a fuel pressure gauge in line to carb one and my stock pump was only putting out 2.5 psi. I have since ordered a new pump and will replace it next. I have new Z therapy carbs which I just balanced and a newly rebuilt and recurved dizzy from advanced distributers. Running new plugs and new coil and a freaking new balast resister that I am bypassing anyway! My car still is very unhappy revving past 4500 rpm.

Check your fuel pressure bud. I wonder if it will help you out. I certainly hope it helps me!

Let's double team this one mizzle !

[Zedyone_kenobi]

When I first installed my Z therapy carbs it pulled like a freight train to 6700 rpm. I see no reason my floats should need adjustment. Bruce had them set perfectly the day I installed them

[madkaw]

Compare notes, but two different situations regarding fuel. Land mizzle isn't running rebuilt carbs!

So when you say it doesn't want to rev beyond 4500- what is it doing? Can you be more descriptive ? Does it sputter, miss out, slowly fade, drop off and pick right back up. Be as precise as you can with words

[Duffman]

Stephen (Kedyone), I am not sure you can get an accurate measure of fuel pressure by running the gauge off of one carb line or the other. I hooked mine up the same way and then realized that with the return line it would make more sense to hook it up right after the fuel pump to get the most accurate reading for both carbs. I had to modify my fuel rail to make the gauge fit after the fuel pump, but believe the reading should be more accurate.

[beermanpete]

Stephen (Kedyone), I am not sure you can get an accurate measure of fuel pressure by running the gauge off of one carb line or the other. I hooked mine up the same way and then realized that with the return line it would make more sense to hook it up right after the fuel pump to get the most accurate reading for both carbs. I had to modify my fuel rail to make the gauge fit after the fuel pump, but believe the reading should be more accurate.

The factory service manual procedure for testing fuel pressure is to use a tee in the fuel line and measure the fuel line with the engine running and return line connected as normal. If the fuel pump output volume is sufficient it will maintain the correct pressure with the return line bleeding off fuel back to the tank. It was designed to do this after all.

As it happens, the pressure should not rise if the return line is blocked due to the design of the pump.

[Duffman]

Beermanpete, I am not disagreeing with you, I am saying that having the fuel pressure gauge off of one of the carb lines does not accurately give the total pressure in the line. You have fuel running into the 2 carb lines and to the return line, if you only measure the pressure to one of the carbs, you are not measuring the pressure to the other carb and to the return line, somewhat incomplete. If you put the fuel pressure gauge right after the fuel pump, you know exactly what pressure it is exhibiting before it gets to the 2 carbs and the return line. I guess I am saying you might have different pressures in each carb line that would not give the accurate reading for the fuel pump itself. Hoping this makes sense.

[beermanpete]

Duffman,

Did you get different readings when connecting the gauge with a tee and then directly?

[Duffman]

Beermanpete, I am not 100% sure, as I have been gettng varied readings at both locations. However, I do see a slightly higher reading when teed right after the fuel pump. I am installing a new mechanical pump as soon as I get a pump spacer this week to see if I have been having pump issues.

[landmizzle]

Hi all,

I don't have a fuel pressure gauge, so I decided to pick up new fuel pump. Figured the worse case scenario is I'd end up with a spare fuel pump. I now have a spare fuel pump. Made no difference.

I did go back and attempt to adjust the floats. You are all right, it is getting easier. The hardest part now seems keeping the gasket lined up while attempting to twist the lids back into position.

Yes, it's obvious when you've set the floats too, high. Gas drooling SUs anyone?

Still, 2nd attempt at adjusting the floats hasn't helped.

It's very possible that I'm setting the floats too low. In the process, I've definitely set them too high (drooling SUs). What is the best way to measure the level? I've seen various diagrams and level settings, but it's still not clear on how to measure the level accurately. For example, I'm assuming the floats are taken out when doing the actual measurement. Otherwise, I'm not sure how you'd measure it.

I've purchased the float level "J" tubes from Z Therapy and used them in the process. The problem for me is that they give you a general idea of the level of the fuel but it's hard to precisely measbure the level (say 1" from below lid) since there is no calibration marks on the tubing nor can you get the close enough to the bowl edge to measure them against. So, I've been eye-balling it as best as I can.

Any suggestions for measuring the levels would be greatly appreciated.

BTW, I have a '72 so my understanding is that the proper levels are different between the front and rear carbs. Is that still the consensus here? I forget the measurements off the top of my head, I just look them up in this forum when I'm ready to do the job. I think it's something like 23 mm front and 17-18 mm rear.

[landmizzle]

I should add that the other way I was trying to adjust the floats was by the using 1/2" drill bit as a yard-stick for the distance between the float lid and he float top. However, I'm not entirely clear if the tab on the float is just supposed to touch the push-pin on the valve (not sure of the actual name) or if it should be pushing it in fully. I think my last attempt was setting it where it was just touching with float gap measured with the 1/2" drill bit. This lead to an arrangement where the surfaces of the top of the float and the bottom of the lid where essentially parallel to one another.

[beermanpete]

If your problem is fuel related it is more likley from poor fuel flow rather than float level adjustment. You should check all the fuel filters. The main filter in the fender of course and the screens in the fuel inlet to each carb (in your favorite float bowl covers). If there is no problem with the filters perform a fuel flow rate test (capacity test) as instructed in the service manual.

[esmit208]

Good food for thought! From everyone