Looks like your slowly getting there Chris. Those jet sizes you have currently installed, still seem rather on the large side. I run 145 main and 45 idle/pilot and a 30 pump jet on a 1434cc A-series.

If you engine is bogging down, sounds like its over fuelling...

edit: Are you able to tune it with the jets you currently have to run lean [popping backfires through the carbs] if so, what jet sizes are they?

cheers
benny

@ ssskiwi

Yeah quite possible Dean. I had a venturi round the wrong way that I found today. Basically it runs like a dog until I throttle the F out of it then it rips into life. Sounds pretty damn good too. Gopt some pretty disapproving looks from neighbors but what the hell they're noise bastards on the weekend nights anyway.

The throttle plates have angular edges but do not incorporate a cutout little cutouts like Webers do. But I suspect they're handed somehow so I'll check them.

I am balancing first body against the last body, skipping 2 & 3. Using an oldschool SU balancer.

venturi in the wrong way will get you every time. basically the main cct is blocked on one cylinder. Is this what was happening Chris?

Hey Benny (@ your first post!),

Yeah if I wind in the pilot screws I get major carb backfiring (even on the PJ70's) and it's hard to keep the engine running unless I'm throttling it. On the 60 pilot jets I had to screw the pilot screws out almost 4 turns to get a decent idle. When I went to 70 I they're around 2 1/2 to 3 turns out and the engine runs smoother on idle when around this range of pilot screw turns.

Manuals insist 2 turns. So I assume the fewer screws (i should say turns) the bigger the feed from the jets.

When I put the big pilots in (unknown size because of the #OOPS# drill bit) but maybe .9mm I got lots of backfires- like exhaust backfires.

When I took the carbs off today I gave them a throttle on their own and they squirted from the nozzles just fine but it did look like a lot (not that I know what to look for). I'm confident that upping the delivery from the accelerator pump has improved the running of the engine but of course I flipped the back to front inner venturi as well so perhaps there's a variable that I should have changed separately.

So yeah, flipped venturi, upped the accelerator arm adjustment so it were to actuate within the range that the manual said. Facet arm on accelerator pump now moves 6mm up and down as opposed to the 2mm or so that it was.

Maybe my jets are all too big except the pilots. The pilot air jets are machined into the body, perhaps I should double check that those are clear?

I've just had a browse for the last hour or so on other peoples jetting lists. Your dead right in saying my jetting is on the big side Benny.

What confuses me is the pilot system, at first with the 60 pilot jets I had the pilot screws out almost four turns to get a decent idle and remove the lean pops. So I put bigger pilots in (which are huge in comparison to typical Datsun A12 with twin webers people are running on here)and I don't have to screw out the pilot screw as much.

If anyone else has any comment on the jetting size of my setup compared to their own, please don't hesitate to make comment.

Are you able to check the progression holes just behind the throttle plate?

If these holes are blocked or partly blocked, then this would effect the transition from idle cct to main cct. But with the larger pilot [idle] jets currently installed, it may be disguising the blockage as the idle jet also would be feeding fuel to the pump cct. Also with the increase of the fuel delivery duration on the pump cct [as you mentioned you modified the accelerator arm] It may be now be over fuelling the mixture via the pump cct.

So many variables in these little animals...

Sounds like the pump nozzle is a fixed size [40] so I guess you will have to tune around it. Are you able to adjust the accelerator arm somewhere in between where it is now and where it was set before? [say 4mm travel]

Be sure to keep track of the changes and the effects you have trialled so far.

cheers
benny

Yeah I reckon I might have to keep a log on them, seriously. Just to keep track.

Okay when I mentioned the bypass before, this is what weber calls progression holes? I checked them but I'll check them again tonight. Those are what I WAS suspecting last time. Otherwise I also think the carbs are jetting too much from the nozzles, not so much in volume but rather the time span of the injection. I read from the 2tg manual that there is only meant to be a 1.5 second injection time span, mine is at least 2.5 when the throttle is opened all the way. Hopefully that will help.

Cheers, should have an update again tomorrow.

Well here is one of the contributors to the poor primary mixture, is this from over tightening?

I didn't check or replace them when I rebuilt them. Though I know they come off all the old mitsubishi carbs so I can race down tomorrow and grab some.

Attach file:

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  Pilot Screws ZOOM.JPG (126.22 KB)

I would adjust the Pump cct duration and nothing else at this stage. 1 thing at a time.. Basically all the pump cct does is to fill the gap between idle and progression /main cct. The pump cct compensates for the sudden change in air flow as the butterfly is opened and the rush of air [lean condition] starts to move. The pump cct tries to level out the trough [see diagram] just after idle
As you probably already know, you only want enough fuel [correct ratio of Air/fuel] and for the minumum time required. By then the progression & main ccts should have caught up and start to meter fuel.

If you haven't seem this chart before, its very handy for a visual of whats going on.