cam selection

[tayto]

sounds good cliff, i will stick with the Howards cam 213/217 112 LSA and keep the hot cam for the boat.

[tayto]

Cliff, I am getting around to rebuilding my carb. Before I went to the Howards cam posted above, you sent a rebuild kit with 73 Jets, 50C rods and an orange spring. Will this be ok with a cam with about 10* more duration?

[Cliff Ruggles]

They will be fine.  The big deal with cam selection is idle tuning.  Once off idle all of these engines make good vacuum at light load and require very similar fuel delivery.  The vacuum production at idle varies considerably, and with larger cams we need larger idle tubes, DCR's, and bypass air......

[tayto]

does anyone know what is float height & other specs for this carb? #17086249

the literature cliff gave me only goes up to 1980, this carb is 1986 (non-CCC)

[Kenth]

Factory float height on this unit is 13/32" +- 2/32".

[tayto]

thanks keith, you have any other specs for it?

[tayto]

never mind I did some serious searching and found it in this document:
https://quadrajetparts.com/pdfs/4009B.pdf

[tayto]

well, it only took 2 years but i finally have the engine together. had some issues with rocker studs (not enough thread engagment with my roller rockers) so i had to pull them off and have them machined and tapped. machinist took pity on me and allowed me to do them myself on his machine. in exchange I had to do the exact same to a set of camel hump heads for him. Was there all day but it was a good learning experience. I take the engine to the dyno on Monday morning. if successful it will be going back in my truck which is currently waiting for its new drivetrain.

Cliff, I had tried to text you awhile back but the machinist had recommended to advance the cam a degree or 2 to compensate for chain Stretch. dont know if this was the right thing to do or not but I did it and we will see how it turns out. (cam has 106 ICL vs 108 ICL). will keep you posted in dyno results.

[tayto]

Well, almost a year later and back on the road. Had no oil getting to my rocker arms last summer which I discovered on a road trip. Limped car home and tore engine apart and went back to machine shop. after some testing we found oil was pouring into the top of the intake valley from the lifter bores. Found GM had drilled some weird counter bore 3/16” into the lifter bore. Block was out if an 87 GMC,had roller lifter provisions bit came with a flat tappet cam. Anyway, having read various things the machine shop decided it would be best to just get a new block. Got engine back in January and started picking away getting it back in. Probably would have had it on the road back in April, but a LOT of screwed up and/or late parts orders. Anyway it's on the road again. BTW, cliff I set the cam to the cam card and DID NOT advance the cam 2*. It actually didn't seem to make any difference on the engine dyno.

Now onto why I posted. Need some help with idle tuning. Carb #17086249 cliff's kit with 73 jets and 50C rods. 355, .034" quench, TBI heads, 213/217 112 LSA cam, on the engine dyno made max power @ 26* total timing. Currently have initial @ 7* (+19 = 26* total). Haven't messed with dist curve yet. Currently making about 15" of vac at idle. My idle screw is turned in so far it is almost coil bound, so i am thinking I should add some idle air bypass? Also the idle is not consistent,it floats. You can actually hear it when sitting at a stop light with the windows down,it will sound ok then the tone changes and drones then goes back to normal and repeats. I did not measure anything when I rebuilt carb 2+ years ago, but everything is STOCK aside from the jets&rods.

[tayto]

here's the weird counter bore on my old block if anyone is interested

[Glutenfreecarbs]

Nice dyno results Tayto! I always figured TBI heads would make excellent low-end torque with the right cam.

Sorry to hear of your idle issues. Are you using vacuum advance? Do the mixture screws have any effect?

And I would NOT run more than 24° total timing under any kind of load with those heads...at least not with American 87-octane gasoline.

[tayto]

I have vac advance, currently on ported.I think I have 6-10 degrees,I have not messed with it since last summer. Have control with mixture screws,can definitely slow and speed up the engine. I dyno'd it with (canadian) Shell 91, current have 89 in there and it doesn't seem to mind it @ 26* all in... It's been very hot here lately 95-100*f  and no audiable detonation.

[tayto]

Opened idle mixture screws from 0.063" to 0.089". Upon taking carb out of service found i forgot to tighten the tube nut for the brake booster vacuum supply. Got my idle screw backed out a bit, and in-gear RPMs down to 550. Still have that random surge,all though it seems to be less now. Find it hard setting my idle mixture screws as the surge moves the needle. They're currently at about 5 turns out, but as I turn them in vacuum goes up slightly but hard to distinguish,sitting at about 12" in gear currently. Tried tipping in the choke and surge is still there. My timing curve starts coming in around 800 rpm. Not sure where to go next.

[Cliff Ruggles]

I'd try stronger distributor spring(s).  In almost all cases fluctuations and surging in engine speeds at idle are the timing is not ROCK solid below 1000rpm's.

I see this a LOT as nearly every troubled vehicle that comes in here for idle issues and carb work has some attempt with cheap offshore distributor spring/weight kits to get all the timing in early.

Every offshore distributor I've seen being sold these days also uses something similar and most do NOT pull all the timing out when the engine returns to idle speed.

I actually LOVE those parts, they have helped keep my wallet full for at least 40 years now by charging folks to remove all that junk and put the stock/correct parts back in place!.......

[tayto]

I have 2 extra GM distributors, will check tonight for stiffer springs. I took truck on a little road trip Yesterday and got some rattle going up about a 1km Long steep incline. about halfway up i went from heavy throttle and back off then went WOT and it shifted down to 2nd and i heard rattle. Sounds like a tip in issue, but wondering if I may have to lower my total timing. I currently have no vac advanced hooked up as I am trying to only do 1 thing at a time and not confuse myself.