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nasty bog on take off
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Author:  powerwagonpaul [ Sat Oct 24, 2009 5:43 am ]
Post subject:  nasty bog on take off
hello all, this is a great forum. i have been visiting for a while and just joined. lots of great stuff here.
my car is a 71 valiant 4dr, i have had it for about a year and a half. the po had just rebuilt the engine and couldnt get it right (actualy i think he bought it that way, the title was not in his name, and he was missing a few bricks :P ) i drove it home on 3-4 cylinders. after setting the valves, rebuilding the carb and replacing the fuel pump( had been sitting a while), i have been driving and enjoying it.
the engine has .030 over flat top pistons (had the head off a few months ago), unknown cam, stock size valves(backcut??), long tube headers and a holley 1920. i am getting about 22mpg on the hiway and about 19.5 around town. it passes smogand runs great.....mostly, it has a nasty bog on take off, other than that nasty bog on take off it runs like a raped ape.
i have been reading the thread on how to drill the idle air passage in the air horn and i THINK thats what i need. how much should i play with the dizzy springs(electronic, not points), and jetting before i come back to this carb mod? pump shot looks good i can feel the power valve kick in at about 10.5in and 5.5in, so the carb seems ok but i cant get rid of that bog on moderate take off. if i granny it, or if i romp on it, no bog, but if i try to take off at a comfterable pace it falls flat, no vacum no power nothing, till i romp on it.
this sounds like what Ted, Mitch, and Juan were experienceing before modifying the carb idle air inlet. is this what i need??
thanks guys,
Paul
Author:  Aggressive Ted [ Sat Oct 24, 2009 9:55 am ]
Post subject: 
Paul,

I fought that for awhile....but first

What main jet are you running in the 1920?
What is your initial timing set at?

Some thoughts....
Sometimes you can get a blockage in the economizer body, have you pulled it recently to clean it?
Sometimes a simple float adjustment will change subtle problems like that. If the gas level is too low in the fuel bowl.....
or if your running a fuel pressure regulator at too low a setting they can't keep up......
Is the mixture screw super clean with no blockages?
Sometimes you can blow stuff out by squirting cleaner down the idle air bleed with the mixture screw pulled.... that may clear it.
Other than that it sounds like there is some slop in the accelerator pump linkage to where it isn't engaging right away. There should be zero slop. Try and rebending the linkage to tighten it up a little and go for max throw on the hole selection.

On medium take offs like your describing mine feels very positive and pulls hard now even on 5 cylinders......amazing! I only have 40 psi in #6 right now. 125#s in the other 5 cylinders....When all 6 where running it would pull hard and would want to go sideways if the front wheels were not straight. So you can dial it out.

With my engine build these are my 1920 mods.

EconoMaster 1920 Holley R7585 modifications:

Reference: .078 = 5/64th
Idle mixture hole .080
Idle bleed #65 drill, .035
Squirter hole #65 .035
Idle @ 3 to 4 turns with #60 to #64 jet
Author:  powerwagonpaul [ Sun Oct 25, 2009 6:24 am ]
Post subject: 
Ted
good thoughts for sure. i have not pulled the economizer body lately however when i did last year and blasted it good with carb cleaner it made no difference, if i can find a gasket ill do it again. i had checked the float level and got it right there, ill double check it. i am running the stock fuel pump regulator setup, do i need more? as far as cleaning the passages and screw holes, i have blasted at least a half dozen cans in and on on all the holes and passeges, dunked it when i rebuilt it after purchase, if its not clean.....maybe i could snug the linkage up a bit but if i change holes for more throw, it blows black smoke, (too much)
not sure what jet size i have on there but which way would you go? up or down? the timing is set by ear, the timing marks dont line up with the balancer mark (different block? mine is a 6830? if thats the right number) i have timing set far advanced as possible without any pings under full acceleration. i see you have yours set by the numbers, if you tell me why and how you got there i could try to replicate that.
it runs great except for that hesitation. i feel like it is defenatly in the carburator, it seems you have gone thru all this with yours and came back to this idle air bleed. mine is plugged up with lead like yours was. if i can change jetting and solve the problem, without drilling, all the better. i do like your description of feeling like a 318. can i get that with jetting alone? eventualy i would like to go two barrels, maybe an 1 1/2in BBD, or that holley 2300, but for now i need to get this 1920 working. i may even keep it if i can get it running right.

going on a poker run with the local mopar club here in las vegas, should be alot of fun. the last time we went on a poker run was this years mopars at the strip. we take the power wagon on the off road jeep run. its fun waiting on jeeps :lol: we got all the right cards and won a model of a new chalanger signed by chip foose. its getting light out now so i need to go wash the valiant.
thanks ted for your advice
Author:  Aggressive Ted [ Sun Oct 25, 2009 8:03 am ]
Post subject: 
Paul,
Quote:
ill double check it. i am running the stock fuel pump regulator setup,
If you have a fuel pressure regulator in line with the pump to the carb, it could cause the bog. I have never had much luck with running one....
Your needle and seat should handle the 6 lbs. easily that a stock pump puts out.
Quote:
if i change holes for more throw, it blows black smoke, (too much)


The pump shot should not effect it that way. If that is true then your main jet is too big and your running too rich or the choke is not open all the way. You may be experiencing a rich bog.....How do the plugs look? Black or light tan?
Quote:
I see you have yours set by the numbers, if you tell me why and how you got there i could try to replicate that.
My block is a 74 with a stock damper and timing chain cover. Just set the initial timing at 12 degrees with a timing light. I recurved the distributor for another 20 degrees of advance and bought a VC-208 can for another 22 degrees.
Author:  SlantSixDan [ Sun Oct 25, 2009 10:38 am ]
Post subject: 
After several decades the 1920 metering block can degrade past the point of no return due to internal corrosion clogging up passages and closing off tiny holes, internal check balls no longer seating, etc.

I still have a few new (not "remanufactured") carbs on the shelf; send me a PM if you'd like one. If you want to keep working with the one you have, I have one (only one) new 1973 non-smog export metering block for the 1920.
Author:  Doc [ Mon Oct 26, 2009 11:29 am ]
Post subject: 
Make sure your vacuum advance "can" on the distrubutor is functional and working correctly.
DD
Author:  powerwagonpaul [ Mon Oct 26, 2009 12:17 pm ]
Post subject: 
i double checked the float level and it was a bit low. the plugs look great light tan, except 1&6 just a slight blackness on one side of the electrode. seems better but ill drive it for a a few days. i am running a #55 jet, seems a bit small (las vegas, 2000ft or so) might bump up a size or two. as far as the dizzy can, it starts moving at about 9in, and stops at 14 or so. not sure whats right but thats what i have. i dont know much about advance curves(yet), so i dont know what im looking for there, but it seems
Author:  Wizard [ Mon Oct 26, 2009 3:18 pm ]
Post subject: 
Interesting, even this is all in idle circuit at takeoff the float level still matter much, even that little of a difference in fuel bowl level?

If it is a bit lean and main jet is correct, if I either press normally or quickly on pedal should I feel bit more surge of power while pump shot is spraying?
Mine does not feel "power surge" at mid to high speeds, only take off I have a bit of bog like Powerwagonpaul is having. Exactly.

Cheers, Wizard
Author:  powerwagonpaul [ Tue Oct 27, 2009 5:15 am ]
Post subject: 
sorry guys, had my step daughter over yesterday afternoon, got sidetracked and didnt even finish my thought before it got posted. that girl has the "look at me dad" syndrome :lol:

i dont think my problem is ignition related because the vacume drops to nothing when it falls flat. seems fuel related to me.

after driving accross town twice last evening, the bog is all but gone, just a slight hesitation, hardly noticable, and not every time. vacume seems up about a half inch. so it would seem that float level is indeed "that important". i wil probaly try going up one size on the jet and see if that solves it, once and for all. i might still try and drill that idle air inlet. if that will give me a bit more out of this 1920 what the hey! i can always plug it back with a soldering iron, if it dont work. maybe ill.......

thanks guys for your input, i knew someone would point me in the right direction
Author:  Doc [ Tue Oct 27, 2009 8:38 am ]
Post subject: 
Did you try giving the engine more initial timing advance?
I may have missed it but where is the inital timing currently set and what is the manifold vacuum reading at idle?
DD
Author:  powerwagonpaul [ Tue Oct 27, 2009 9:14 am ]
Post subject: 
doc
timing is set as far adavanced without any ping under full acceleration. the marks from the dampner dont line up with the marks on the timing cover. i had to change dampner and i must have got one from a different aplication. im running 91 octane. vacume is 19 out of gear and 16-16.5 in gear

thanks
paul
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