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Mon Jun 23, 2025 7:34 pm

I have a 1979 bus with a 2.0 motor and dual carb set up. Just installed the motor the other day. Bench set the carbs empi hpmx 40, has spark but won’t run on one and two. I rechecked gap in plugs and reset the idle and mixture screw, any recommendations? Thank you

Mon Jun 23, 2025 9:12 pm

Maybe dump some fuel injection cleaner down into the bowl vent on the 1-2 carb and let it sit for a day or two. If the cabs sat for months with ethanol laced fuel rotting in the bowls, disassembly and cleaning may be required. Which gasket did you use between the manifolds and the heads? The thick fuel injection style gasket can end up sitting on the tin sometimes causing a vacuum leak.

Ignition wise have you checked for a cracked distributor cap? If the 1-2 wires are crossed it should backfire badly.

Tue Jun 24, 2025 2:53 am

Sounds to me you may have an intake leak. It’s tough bolting dual carbs down. Easy to end up with them sucking air on one side or the other. Use carb cleaner or brake clean. Spray all mating surfaces if it’s sucking air. It will tell you where.
Happens all the time. Easy fix.

Tue Jun 24, 2025 4:32 am

Quote: Maybe dump some fuel injection cleaner down into the bowl vent on the 1-2 carb and let it sit for a day or two. If the cabs sat for months with ethanol laced fuel rotting in the bowls, disassembly and cleaning may be required. Which gasket did you use between the manifolds and the heads? The thick fuel injection style gasket can end up sitting on the tin sometimes causing a vacuum leak.

They are brand new carbs I went thought and bench set everything and cleaned them.

Tue Jun 24, 2025 4:37 am

Quote: Sounds to me you may have an intake leak. It’s tough bolting dual carbs down. Easy to end up with them sucking air on one side or the other. Use carb cleaner or brake clean. Spray all mating surfaces if it’s sucking air. It will tell you where.
Happens all the time. Easy fix.

I did pull the plugs and they smelled of gas, if there was a leak would it not ignite the gas? I’ll try it [/s]

Tue Jun 24, 2025 4:52 am

Tbrier100 wrote: Quote: Maybe dump some fuel injection cleaner down into the bowl vent on the 1-2 carb and let it sit for a day or two. If the cabs sat for months with ethanol laced fuel rotting in the bowls, disassembly and cleaning may be required. Which gasket did you use between the manifolds and the heads? The thick fuel injection style gasket can end up sitting on the tin sometimes causing a vacuum leak.

They are brand new carbs I went thought and bench set everything and cleaned them.
Is there fuel inside the 1-2 carb for sure and the acceleration pump system also operates properly?

The firing order is correct?

Are only the carbs new on that engine, or more ignition parts?

Valve adjustment OK?

Tue Jun 24, 2025 5:36 am

Quote:
Tbrier100 wrote:
Quote:
Maybe dump some fuel injection cleaner down into the bowl vent on the 1-2 carb and let it sit for a day or two. If the cabs sat for months with ethanol laced fuel rotting in the bowls, disassembly and cleaning may be required. Which gasket did you use between the manifolds and the heads? The thick fuel injection style gasket can end up sitting on the tin sometimes causing a vacuum leak.

They are brand new carbs I went thought and bench set everything and cleaned them.

Is there fuel inside the 1-2 carb for sure and the acceleration pump system also operates properly?

The firing order is correct?

Are only the carbs new on that engine, or more ignition parts?

Valve adjustment OK?

The top end of the engine was rebuilt, new pistons, rings, jugs, heads and new valves, bottom was solid. I rechecked the valve adjustment. the lifters are hydraulic and I bled them before putting them back in. I bought a 123 ignition distributor but couldn't get it to fire right so borrowed my friends extra distributor and now we have it running on two cylinders. the carb I did not check that. the pump system works good, when I pulled the plugs on that side to check them they smelled of fuel.

Tue Jun 24, 2025 5:54 am

how does the compression feel for those two cylinders.

Tue Jun 24, 2025 5:57 am

Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test

Tue Jun 24, 2025 6:27 am

Tbrier100 wrote: Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test
Is the feeling of compression about the same on all 4 cylinders?
What is with the dizzy and I-system before new built up?
(dizzy shaft bent, contact not opens on 2 cylinders?)

Tue Jun 24, 2025 6:37 am

wagen19 wrote: Tbrier100 wrote: Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test
Is the feeling of compression about the same on all 4 cylinders?
What is with the dizzy and I-system before new built up?
(dizzy shaft bent, contact not opens on 2 cylinders?)

Shaft doesn’t seem to be bent. How would I i know that? Compression feels pretty close on all from what I can tell. Contacts on distributor?

Tue Jun 24, 2025 7:43 am

Tbrier100 wrote: wagen19 wrote: Tbrier100 wrote: Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test
Is the feeling of compression about the same on all 4 cylinders?
What is with the dizzy and I-system before new built up?
(dizzy shaft bent, contact not opens on 2 cylinders?)

Shaft doesn’t seem to be bent. How would I i know that? Compression feels pretty close on all from what I can tell. Contacts on distributor?
you think I should do a compression test?

Tue Jun 24, 2025 8:04 am

maybe spray a little fuel into the carb while cranking,a drop of oil in the cylinders may help with compression,use a blow gun in the spark plug hole to blow the oil around in the cylinder

Tue Jun 24, 2025 8:23 am

Tbrier100 wrote: Tbrier100 wrote: wagen19 wrote: Tbrier100 wrote: Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test
Is the feeling of compression about the same on all 4 cylinders?
What is with the dizzy and I-system before new built up?
(dizzy shaft bent, contact not opens on 2 cylinders?)

Shaft doesn’t seem to be bent. How would I i know that? Compression feels pretty close on all from what I can tell. Contacts on distributor?
you think I should do a compression test?
My thinking is to check, if the contact in dizzy opens properly on all 4 cylinders.
I had once issues, sparks not on all plugs, because the contact in dizzy had not opened on all cylinders. (due to wear in bearing of dizzy and slightly bent shaft.

After a compression test on all 4 cylinders, you would have clear insight of inner pressure and mechanical condition.

Of course OK must be:

1.) mechanical parts, valves, compression
2.) ignition, timing, no too hight resistance in spark plug wires and connectors
3.) fuel, pump, lines, carb, air filter (not plugged)
4.) exhaust system not plugged (very rare issue, but not to forget)

I had several times issues with one not opening or semi plugged needle valve on dual carb set ups.

Tue Jun 24, 2025 10:53 am

wagen19 wrote: Tbrier100 wrote: Tbrier100 wrote: wagen19 wrote: Tbrier100 wrote: Quote: how does the compression feel for those two cylinders.

from just turning the motor I can feel it. but the rings are not bedded in yet so I haven't done a compression test
Is the feeling of compression about the same on all 4 cylinders?
What is with the dizzy and I-system before new built up?
(dizzy shaft bent, contact not opens on 2 cylinders?)

Shaft doesn’t seem to be bent. How would I i know that? Compression feels pretty close on all from what I can tell. Contacts on distributor?
you think I should do a compression test?
My thinking is to check, if the contact in dizzy opens properly on all 4 cylinders.
I had once issues, sparks not on all plugs, because the contact in dizzy had not opened on all cylinders. (due to wear in bearing of dizzy and slightly bent shaft.

After a compression test on all 4 cylinders, you would have clear insight of inner pressure and mechanical condition.

Of course OK must be:

1.) mechanical parts, valves, compression
2.) ignition, timing, no too hight resistance in spark plug wires and connectors
3.) fuel, pump, lines, carb, air filter (not plugged)
4.) exhaust system not plugged (very rare issue, but not to forget)

I had several times issues with one not opening or semi plugged needle valve on dual carb set ups.

I will try all this tomorrow and report back, thank you

Tue Jun 24, 2025 11:29 am

Look down the carb throats using a mirror while the fuel pump is running or just after shut down. See if fuel is just dumping into the engine. If so, the extra fuel will drown out any attempt at combustion.

Tue Jun 24, 2025 11:32 am

aeromech wrote: Look down the carb throats using a mirror while the fuel pump is running or just after shut down. See if fuel is just dumping into the engine. If so, the extra fuel will drown out any attempt at combustion.

I will check, I’m not new to cars but I don’t know carbs at all or much old school stuff. I have a fuel pump that puts out 2.5-3 psi of fuel. I will check that. Thank you

Tue Jun 24, 2025 11:41 am

check your plug wiring again. Most likely 1 and 2 are reversed. If not spray a little berryman's b12 down the carb and see if all 4 run for a second.

Tue Jun 24, 2025 3:12 pm

Just yesterday we were working on a Porsche 356 kit car based on a 1967 Ghia. It’s been parked in a garage for several years. Once we drained the tank, replaced the Facet electric fuel pump, and installed new fuel lines and filter we tried to start it.

It ran but not very well. Checking the carb synch using a snail, we found that 1&2 side Weber had almost no flow while the left carb was working. On further inspection we found that the right side carb was missing the idle adjustment screw. We believe this caused the throttle plates to be completely closed and is the source of the problem.

One call to Justin at Blackline Racing in Idaho and we have a new screw and spring in the mail due Friday. Thank you again Justin.

I’ll try and get back here soon with any results we come up with.

Tue Jun 24, 2025 5:44 pm

aeromech wrote: Just yesterday we were working on a Porsche 356 kit car based on a 1967 Ghia. It’s been parked in a garage for several years. Once we drained the tank, replaced the Facet electric fuel pump, and installed new fuel lines and filter we tried to start it.

It ran but not very well. Checking the carb synch using a snail, we found that 1&2 side Weber had almost no flow while the left carb was working. On further inspection we found that the right side carb was missing the idle adjustment screw. We believe this caused the throttle plates to be completely closed and is the source of the problem.

One call to Justin at Blackline Racing in Idaho and we have a new screw and spring in the mail due Friday. Thank you again Justin.

I’ll try and get back here soon with any results we come up with.
There's an excellent HPMX set up guide on You Tube. It goes into detail about idle set up at minute 5:00 or so.
The Redline Instructions mention shoving a .004" feeler gauge into the carb base to set the throttle blade(s) via the idle stop screw. All else is done via mixture screws & jetting changes.