TR5/TR250 At wits end TR250 missing

[Got_All_4]

I'm probably very late in getting this posted but I tried do figure it out myself. 90+ % of the time I'm right. What started out as a slight miss while at cruising speed into a pretty good miss at acceleration. When getting up around 3800 rpm is when this miss really starts to be a problem. If I try to go to higher revs it usually won't go past 4200 rpm.

What I've done; balanced the carbs a bunch. Changed sparking plugs and wires. checked timing. (New Pertronics) Discovered that the choke was on a bit so I released the cables some. Blow out the fuel lines with compressed air. Filter too. While watching the motor run with the air cleaners off some fuel puked out of the over flow in the 3rd carb. Took the carb off and there was a piece of rubber hose stuck between the jet and the paddle. Replaced all the fuel lines with steel and I had an extra carb rebuild kit too so I replaced the float jet in the 3rd carb. Then the 2nd one started to leak. So off they all came and a thorough cleaning and replaced the 1st and 2nd carb jets too. I set the floats to 17mm off the edge. Still not there yet. I does run nicer down the road but once you try to accelerate it brakes up.

Does seem now to be a fuel problem. My next thought is fuel delivery is not adequate. I replace the mechanical pump with an electric one and I wonder if it's going bad. This needs to happen fast as we are planning to go to TRF summer party on Thursday. Thanks!

 

[TR3driver]

If it's fuel delivery, then the engine will rev higher with no load than with full load. It will also take a beat to "catch it's breath" after you back off the throttle (as the float bowls refill). Ignition problems are usually somewhat less specific about load (although they still tend to show up more under load), and any changes are generally more instantaneous.

From your description and my recent experience, I'd try swapping out the coil and maybe even switching back to points. I removed the new Pertronix from my TR3, and it runs a LOT better without it.

 

[Deleted member 8987]

All of that.
Originally 2 carbs, right?

So, you have a higher-flow fuel pump for 3 carbs?

I have seen that odd miss and lack of high speed before with coil primaries reversed.

There used to be a way we checked it without a scope in the old days using a lead pencil.

Hold the pencil tip between the end of the plug wire and the plug or head while running......the flash should go towards the head.

Other than that, if you know someone with a scope, all the firing peaks should be upwards and not down.

Dave

 

[DNK]

Whew, I thought someone stole your 250.
That's a relief.
There's a lot of people running 3 stroms on a stock pump.
Pretty sure Ken and Paul are.

 

[HerronScott]

Whew, I thought someone stole your 250.
That's a relief.

I was thinking the same thing from the title!

Scott

 

[luke44]

...From your description and my recent experience, I'd try swapping out the coil and maybe even switching back to points. I removed the new Pertronix from my TR3, and it runs a LOT better without it.

FWIW I had the identical experience with my old TR6. Went back to points and it was like a new car.

 

[poolboy]

Yeah, as Don mentioned I have 3 ZS on an original type pump. I don't often run WOT, but when I have the pump kept up.
BTW, I've seen Jeff Schlemmer write about "phasing the rotor"
(believe that was the term), whereas the spark was called for past the rotor as the timing advanced.
Have a look at the carbon burn on the rotor. Ideally it would be near the middle. If it's just about on the back side of it's travel, that may be the problem.
Don't ask me how to cure it, Jeff described it, but I don't feel comfortable trying to recall.

 

[Opa]

right on Ken,had that problem myself years ago. Seem there was a bunch of after market rotors where the "tail"on the rotor bar was somewhat shorter than the lucas version. Jeff at advance made up a batch as I recall and BPNW sells Lucas rotors.Should look like this

 

[DougF]

I just installed my triple Strombergs and had a miss that wouldn't go away. I just reset my jets to .110 to lean them out a little. Installed new plugs yesterday, and it seems to be gone. I only ran it for about 5 minutes. I pulled the carbs off for further unrelated adjustments so I haven't run it any more.
When Colortuning, I found there was very little flame in #3 cylinder. The two previous plugs had washed out.
Have you modified your engine?

 

[Got_All_4]

Got the new pump on and going to try it in 15 min.

 

[Got_All_4]

Well the pump didn't cure the problem so I took Luke44's advice and went back to points. Remarkable difference. even the wife said it sounded better as I drove by the house. I still took it to my Triumph mechanic tonight. I'll have him dial it in after all my fiddle faddle.

Yes Doug it is modified. 10:1 comp. cam, roller rockers 155:1, total seal piston rings and ported etc. It does run very well when it's tuned properly.

I'll keep you posted.