Topic: Balancing keyhole cards, almost no vacuum.

[Magpie]

Carb gurus wanted to jump and anyone else with ideas. 1978 F, I'm trying to balance the carbs using vacuum gauges and a Carbtune. valves are set right, same for timing. Engine has never been apart according to the previous owner. 2 turns out on the needle jets.  I have gone through the keyhole style carbs. At first all four cylinders showed no vacuum on the Carbtune and about 4 mmHg on the vaccum gauges.  After much fiddling I have the Carbtune showing what is in the photo below. Number 2 carb is not adjustable and is the "standard" to set too. The accelerator pump is working. The engine is running very hot and started smoking yesterday. I'm at a loss. What do you spray around the carb insulators to see if they are leaking? I tried WD40 with no change in engine rpm. Any hints?  I'm at my wits end. Thanks, Cliff.

[Magpie]

[dave500]

is the ignition spot on?

[BenelliSEI]

Valve clearances OK?

[maxheadflow]

Compression test?

Add.  Plugged metering valve on the gauge?   Hole in hose?  Check the gage first. Swap hoses.

[Magpie]

Ignition good, valves good, compression at just under 150 psi. I'm stumped and going to pull the carbs again.

[BenelliSEI]

Brakleen or Quick Start around the intake manifolds (very little and keep your face away). You must have a massive vacuum leak somewhere?

[Magpie]

I have sprayed around the carbs with Brake Clean with no change. I have also discovered that the accelerator pump is not working properly which is common to all 4 carbs. Sometimes it sprays, sometimes not. I'll order a new one and see if that helps.

[TwoTired]

Do verify your test apparatus isn't lying to you. Swap hose connections temporarily.

The carbs don't make vacuum. The engine cylinder does.

However, I had something similar happen, where carb 2 wasn't reporting much vacuum.  Turned out all the other carbs were synced to each other, but NOT to #2.  That slide was way more open than others.  Had already verified the cylinder and valve health.  So, readjusted each in turn to match #2 and all was well.  But, I was confident the gauges were not lying to me.

Cheers,

[jgger]

I'm not  an expert by any imagination,  but doesn't the accelerator pump work on vacuum? So If you are having vac problems then could that cause the pump to have issues too?

I agree with TT check the gauges and  then maybe a visual on the slide heights.

[BenelliSEI]

I'm not  an expert by any imagination,  but doesn't the accelerator pump work on vacuum? So If you are having vac problems then could that cause the pump to have issues too?

I agree with TT check the gauges and  then maybe a visual on the slide heights.

Smart observation. Seems like a very plausible answer? Curious what you find.....

[ekpent]

 I thought the accelerator pump was more of a mechanical set-up  with a plunger activating off the throttle linkage on the carb rack. No major expert though on pumpers as I only have had one 750 later then 1976.
  You can tell if the pumpers are working by just twisting the throttle whether the bike is running or not and looking for a squirt if the air box is off.

[TwoTired]

78 F does have an Accelerator pump.  It is mechanically actuated.  If number 2 bowl is filled, every time you twist throttle, it squirts all four cab throats.

Cheers,

[samm_j2]

Sounds frustrating, did you bench sync the carbs? Is the bike idling and running? I would think if things are as bad as what isnposted in the picture it would not want to start/idle. Do you have access to another carb sync tool to try out?

[ekpent]

 When rigged up correctly the Morgan Carbtune has a type of restrictor in the line to each carb that if I remember I had to install by cutting the lines a certain length. Like other synch tools they act as dampers for needles,slides, etc. so they don't flutter. Might want to check Cliff to make sure a hose isn't plugged with a little debri in the hose around one of them.

[jgger]

Thanks Lloyd for setting me straight.

[Magpie]

Finally! The common thing to all 4 carbs is the accelerator pump. I know the one in my 77 is working well because the engine starts, idles nicely when it's warm and responds to throttle input. So I took the one from the 77 and put it in the 78. Instant gratification! Snap the throttle a couple of times and have vacuum across all the carbs. The carbs are balanced, the engine runs quieter and strangely cooler. I've ordered 2 pumps from 4into1.
A side note on vacuum gauges and the Carbtune. One of our fellow members, David750f, kindly lent me a Carbtune system. He also dropped by my shop with words of wisdom and encouragement which I much needed during this frustrating adventure into keyhole carbs. It's easy to use and worked well balancing the carbs on my K3. However going back and forth with the Carbtune and the vacuum gauges a number of times on the F, I liked the gauges better. They seemed more visual to me and responded to small adjustments "better" is the only way I can describe it. I may end up getting a Carbtune anyway as I am a sucker for a new tool in the box.
Thanks for all your comments and suggestions.
Cheers,
Cliff.

[Bodi]

I've used gauges, a mercury filled type, and the carbtune. The gauges are nice: easy to read, easy to calibrate (or at least get all 4 reading the same) but pretty bulky and somewhat delicate. The mercury unit was great but once filled with mercury they can't be stored away easily, I think I left it hanging in the basement of a house I moved out of. Carbtune is certainly adequate and similar to the mercury sticks to read, seems sturdy, and is easy to store. But like my timing light and electronic ignition, I have used it rarely as I haven't had the carbs off many times. Last time was 4 years ago when a fuel crossover O-ring fell apart with predictable fuel dribbles.