My '69 427 stumbles and misfires occasionally when the throttle is snapped. Happens whether under load or not. Otherwise it runs strong. The accelerator pump linkage is adjusted within spec and it's timed as per Lars' timing article. Yesterday I pulled the squirter and it's a "non-tube" type stamped with "21" which supposedly means an orifice size of .021". This seems to be on the small side for such a big engine. I'd like to know if it should be up-sized and if so by how much or at least where to start.

Thanks,
-Doug

 

THis is going to be all over the place as a response
Are you running mechanical linkage to open the outboard carbs or the vacuum pods only? Is it the stock camshaft? THe big problem with our tri powers is no outboard accelerator pumps. But there are a number of ways you can try and tune this out. A little background on my motor as your results may vary. My experience is with 3 franken carbs with AED metering block and plates so I can also tune the outboard jets sizes...also its on a 396 so the fuel needs are different. My 427 block isnt due back until next week but I still need to buy heads, gaskets and bearings so the 396 may be in the vette until may or june. I also have an AFR gauge on my A pillar so I can see what is happening as I mash the go pedal. I also had mechanical linkage so I wasnt waiting on any vacuum. I was getting closer to getting mine tuned in but winter came and a number of changes are happening to my motor so all my research will change as well.
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Back to your question....
You can go to springs that will slow the pods opening so you dont go lean right away. IF you just increase the squirter you will give it more fuel in that squirt but just in that instance, Which could give you a rich bog before the secondaires even open. If you change the cam you can change when it is squirting, how much and how long. THe bigger the nozzle size the shorter the duration without it

. THe next thing would be to look at your pump and decide if you want or need a bit more volume as well. They are rated at 30cc and 50cc but that is measured at 10 pumps so you are looking at 3cc and 5 cc volume total unless you keep pumping the throttle to reload the pump.


But For my setup I was gaining ground with the cam change along with the squirter and 50cc pump. What I did was look for a few different charts on the pump duration and went with a longer running cam and slight increase in the nozzle size but not a big one as I wanted to increase the duration of the squirt as well as get a little more to help when the secondairies opened as well. I didnt want to loose all my squirt all at once. I also changed the power valve so that it also gave me more fuel earlier.

I know this isnt the exact answer you wanted but it is a lot of research depending on your setup. I have a good size engine cam as well so that changes the demands on the carbs.

I write everything down I do and try to change one thing at a time so I can see what is helping and what is not. Having the gauge helps a lot so I am not just going by seat of the pants results.

THis go round this spring I have a completely stock setup so I dont have the jet sizes to contend with,. I want to have a record of the stock response to just tuning it with the meter and then modifying it to see where I can get a better response. My old setup wasnt great off the line unless i feathered into it and then mashed it above 3000 rpm but it was getting better off the line

I can update you with my experiences if you like

Go though this info and treat the tripower as a vacuum secondairy 4 barrel. It is just a divorced secondairy system
the first paragraph after the pic of the pump that is titled "Watch these Videos" will start to give you good info

http://garage.grumpysperformance.com...mps-cams.1790/

Just remember that out fuel bowls are pointing the same way as the primarary fuel bowl so the secondairies are not going to starve for fuel

 

If you change the squirter..... DO NOT MOVE THE THROTTLE OR THE NEEDLE VALVE WILL SHOOT OUT AND FALL DOWN INTO THE CARB!!!!

 

WOW, you’ve certainly done a lot of research into this. Thanks for sharing your experience.
Vacuum pods on the secondaries. The engine has an Engle, 560/580 camshaft that produces 13 in. hg. at idle. (see cam card attached below). It's a .030 over stock, "512" block with "990", 118cc open chamber heads.

I’ll try experimenting with a few different size nozzles and cams. The current one is orange.

I'm not looking for optimum performance here, I would just like to fix what I consider to be a minor bug. I was hoping to get a starting point and size suggestions.

I'll be looking forward to what you wind up running in your 427.

 

nice cam. Im going a bit smaller. I need to stay around 500hp/500ftlbs so my tranny will survive. If I blow this up I will go with a richmond 5Speed and then all bets are off Hp wise. but probably would stay under 600hp. My pistons have a -38cc dome and would be about 10.75:1 compression with a 119cc chamber

https://www.compcams.com/factory-mus...k-396-454.html

 

I'd. Start going 5 sizes bigger on the squirter and see if it helps. That's easy to do.