engine backfiring, lack of power

[XJRpilot]

when i start my "B", it starts fine and idles fine but upon giving it some throttle, she backfires through the carbs, between 1000rpm and 2500rpm, yet is fine between 3000 and up out of gear.
she does not have enough power to move when placed in first gear, and stutters, backfires,
and stalls. any ideas?

 

[aeronca65t]

Somtimes bad cap and rotor will cross fire at certain RPMs...make sure plugs wire aren't shorting out too. Good test for plugs wires: start car at night in dark area and "mist" water over engine with plant sprayer...bad wires will make it sparkle like a Xmas tree.

Occasionally, the little multi-strand wire that grounds the points plate will fray and as the plate rotates (due to advance) the wire will "make and break". Same thing will happen even with electronic ignition.

Torn diaphram in ZS carb (if you have ZS).

Check fuel filter.

Could be junk/dirt in main jet discharge port. Remove damper (piston) from carb and "back-blow" through main jet with *light* air pressure.

If it's been sitting for a while, could be sticky valves....running engine for a while may solve this.

 

[Gary Lloyd]

Maybe a lean condition?? Probaly cap and rotor though!!

 

[XJRpilot]

ok, i replaced the dizzy cap and rotor, but it wasnt oe, its borg warner brand. i have not yet replaced the points and condenser even though i have them (whats the condenser for anyway?), i'm wondering if the cap and rotor are defective.
i also replaced the wires with a universal set that is somewhat longer than stock. it also sat idle over much of the winter, so maybe the valves could be sticky. a little lean. hmmm...
thats a possibility to since i tinkered with the
carbs during the "winter to "spring" transition.
you guys are too good! you pinpointed everything i did, so i'll just backtrack. one more important thing: when she is warmed up and idling, i try the piston lift method to determine rich or lean
on the carbs, but there is no change in idle.
the pistons are moving freely though.

 

[XJRpilot]

went out to tangle with the b this morning, no start. getting spark , fuel is iffy. the rear carb flooded while the front one stayed dry. have to scratch my head on this one. i hate these carbs. another thing, my flashers only work on the left side. right side nothing. lucas curse? i checked all 4 fuses (chuckled at that one) in the engine bay, all ok.
is there another fuse inline somewhere? or is the flasher kaput?

 

[Bruce74B]

Two suggestions for two problems. Drain the float bowls on the carbs and clean em out good for the running problem. As for the four-ways only working on the left side, pull and clean the switch connections...had the same problem on my 74B. Good luck

Bruce

 

[XJRpilot]

cleaned the four way connections, all is fine.
flashers work fine now.
the b started this morning, but runs like crap.
no backfiring through the carbs though. thats a good thing. i replaced the condenser, points, and wires. new dizzy cap and rotor. i cleaned the carbs with 2 cans of carb cleaner( sprayed the heck out of them inside and out). i replaced the old damper oil with fresh mm oil , and adjusted the float level using my 1/8 drill bit. its getting fuel, but i definitely need to tune the carbs.
i get the feeling i'm SU challenged. i cant seem to get the "hang" of it. i need to find the SU challenged version of tuning the carbs rather than the bentley manual.

 

[aerog]

The SU book that Moss sells is worth buying. It covers all the SU carbs (and fuel pumps), but is much more comprehensive than the Haynes and Bentley books.

If you didn't do it (sounds like you did), take the covers off the carbs, pull the pistons, and clean them away from the car in a tray. I use carb cleaner and a toothbrush to clear away any varnish, then reassemble.

 

[XJRpilot]

pistons pulled and cleaned, along with every thing else. heres where i am:
engine starts fine. i started step by step
instructions in the bentley manual for basic tuning dual HS4 carbs. slackened all nuts on connecting rods, and started to adjust for idle using the idle adjusting screws. it idles a little choppy, with some backfiring but it idles around 500-800rpm.
i balanced the carbs using the unisyn
and the idle adjust screws and they are balanced. when it idles fine its great. all of a sudden it will shoot up to 3500-4000 rpm and stay there. i have to shut off the engine, and restart it then it idles choppy again. then it will idle ok for a while then it rises up to 3500-4000 again. i replaced the needles with grose jets, and i'm positive there is no "grit" in the carbs since i cleaned the carbs fanatically. anybody have a clue?

also the new header i installed was glowing red at the collector junction. what does that mean?running to rich or too lean?

[ 04-17-2003: Message edited by: XJRpilot ]</p>

 

[XJRpilot]

i was wondering, that since i installed a rebuilt rocker arm assy, would adjusting the valves have a serious positive impact on the carb tuning process?
just a thought.

 

[XJRpilot]

i'm checking into faulty grounds/connections.
my fuel pump is a replacement facet solid state.
i do have an adjustable fuel pressure gauge set to 3psi.
its a noisy bugger, but the noise has changed its "tone" lately. i checked all fuel filters. i have one between the tank and pump, and one between the pump and carbs. i think it could be a possibility that the fuel pump wiring is the fault between the pump and the fuse. or even possibly corrosion on the fuse connections which is creating a on/off/on/off ect.. condition. i have no way of checking the psi output, but at one point it strained to fill the clear fuel filter. at other times it fills it with no problem. sporadic operation definitely. electricity problems can cause some wierd phenomena, especially if its fuel delivery related. i'll adjust the valve lash, and see if that helps the carbs second. (it needs an adjusment anyway).

i forgot to add: if after the fuel pump check all else fails i'm going to a weber 32/36 dgv carb.
and use the su's as bookends.

[ 04-19-2003: Message edited by: XJRpilot ]</p>

 

[Dave Russell]

XJR,

I am quoting from a couple of your previous posts--

"instructions in the bentley manual for basic tuning dual HS4 carbs. slackened all nuts on connecting rods, and started to adjust for idle using the idle adjusting screws. it idles a little choppy, with some backfiring but it idles around 500-800rpm."

"all of a sudden it will shoot up to 3500-4000 rpm and stay there. i have to shut off the engine, and restart it then it idles choppy again. then it will idle ok for a while then it rises up to 3500-4000 again."

"also the new header i installed was glowing red at the collector junction. what does that mean?running to rich or too lean?"

These are all symptoms of retarded ignition timing Especially the hot collector.Try checking & setting the timing, or for a start just rotate the distributor for fastest idle & reset it to exact specs later.

"i was wondering, that since i installed a rebuilt rocker arm assy, would adjusting the valves have a serious positive impact on the carb tuning process?"

Yes, incorrect valve lash could be a partial cause of your problem. Wouldn't hurt to check it.
D

[ 04-19-2003: Message edited by: Dave Russell ]</p>

 

[kmcormick9]

im having the same sort of problem in my 76 midget. i replaced plugs and wires last year. it started for me when i replaced my mechanical fuel pump. i tried replacing the fuel filter which had a marginal improvement. later, while me and my friend were toolong around he tapped the top of the pump with a wrench and it seemed to fix it. it ran great for about a week and then started doing it again. any ideas on a single stromberg car?

 

[XJRpilot]

after much fiddling and troubleshooting,
it turns out the points were shot. installed new points and strobo timed the engine and it purrs now. runs great. thanks guys, if anything i learned a whole bunch of new things while fiddling about. at least my carbs are tuned real well now. took some reading but i did it.

[ 04-27-2003: Message edited by: XJRpilot ]</p>