Hesitation under load - 3 x DCOE

[Tj]

Hey guys, Just finished dropping in my new engine and I'm coming across a hesitation issue under load (acceleration) and I just wanted to run a few ideas past you before I start pulling things apart again.

 

First off, a little about the engine.

I bought it of Stevo_gj who bought it off Tyson a while back, heres the for sale thread with all the particulars in it: CLICK HERE

 

Anyway, it starts, it idles, it revs freely (once warmed up of course) but when driving it, even the slightest bit of throttle makes it bog down. I've tried gently and slowly rolling on the throttle and also tried driving through it but it doesn't clear.

 

There's a few other issues that I know I need to rectify but I don't know if they're the cause.

Firstly the manifold gasket is stuffed and I've proved it has a leak on the centre carb. I have a new gasket but the ports are too small. Can someone like Stewart Wilkins enlarge them? or do I need to track down someone who makes them bigger?

Also, It's running some sort of aftermarket fuel pump but I don't really have any way of checking pressure or flow. I'm waiting to hear back from Gareth to hear if that Carter pump he has for sale is the 4070 that comes highly recommended, If so, I'm going to jump on it.

Finally, the throttle linkage shaft is not quite right. The bearings on it are a bit seized up making the throttle hesitant to return to idle. I've got a heavy return spring on it while I'm fiddling with it but it doesn't work the best. Could this sticking shaft be twisting the linkage shaft making the carbs open out of sync?

 

Also, the electronic dizzy that came with the motor is missing a few bits (that I haven't had a chance to chase up with steve yet) so I'm running the original points dizzy off my old stock engine. I know it works because it was running fine on the old motor. I know it needs to be re-weighted but if I'm going to fiddle around with a dizzy, I'll get the electronic one working again.

 

Now, Dad has set the carbs up and he's fairly good at it. As I said earlier it revs quite freely without any fuss while parked out of gear, but its when I try and accelerate putting the engine under load that it doesn't play along.

We advanced the base timing a little today and it improved it but not completely. We're reluctant to advance it too far though to avoid pinging.

 

Is there anywhere else I should be looking?

Thanks guys.

[Scoota G]

Need to know jet sizes, air correctors, idle jets, emulsion tubes. Your biggest problem which is points ignition. Many a problem with triples will be solved with electronic ignition.

 

I run triple 45MM DHLA's on mine with an auto.

[Lynton]

My experience is limited to twin side draughts however check gaskets at the carby manifold aren't sucking air, a points distributor on Zeds have notorious points bounce under load stick with electronic dizzy. The manifold gasket tp the exhaust could definetly be unbalancing the triple setup. I doubt it is the petrol pump as it revs freely.

just my 2 cents worth, by the way I had a similar problem on my zed and it turned out to be a fusible link wire breaking down.

Regards Lynton

[d3c0y]

Well for a start fix all your manifold leaks because if they are inlet leaks they will be effecting the mixtures. I used to run no manifold gasket and just used RTV red silicone when i put it back together and it ran fine with no leaks. No worries about the ports then too.

 

How old is the fuel in your car and are you running it on 98 octane fuel?

Have you synced all the carbs with an airflow/manometer?

Was the car running carbs before? Triples only want like 3 - 4psi of fuel pressure and are sensitive to this.

Have you checked the plugs to see if it's rich or lean?

Does it blow black smoke when you drive it?

 

If you have new points in the dizzy and they are adjusted properly it should be fine if it was working before.

What is your base timing set to? Do yourself a favour and get a CDI like an MSD or Crane. I run a Crane HI6 with the points still and it runs smooth and strong all the way till, um i shift gear because my tach doesnt work because of the CDI!! haha

[NZeder]

I run a Crane HI6 with the points still and it runs smooth and strong all the way till, um i shift gear because my tach doesnt work because of the CDI!! haha

sorry for the off topic move on this post but this will help with your tach issue.

 

http://www.dinoplex.org/tachoconversion/index.html

[chris240]

Exactly what Mark / scoota said, we need to know the recipe of whats in the carbs, then well go from there.

Mind you try to fix those other 14 minor items you described !!

[d3c0y]

sorry for the off topic move on this post but this will help with your tach issue.

 

http://www.dinoplex.org/tachoconversion/index.html

 

I've already bought all the parts x 5 for that but need a 10,000rpm tacho now so i just bought a 5" tach off ebay instead.

 

Would really like to get a hold of a pivot 5" but they are $200 :/

[Scoota G]

Run the stock fuel pump with triples, make sure it has a new kit. Never had a problem with fuel pressure.

[luvemfast]

Apart from all the other issues.

My guess is it's running rich.

[Tj]

Exactly what Mark / scoota said, we need to know the recipe of whats in the carbs, then well go from there.

Mind you try to fix those other 14 minor items you described !!

 

Sorry guys, got a little busy this week.

I did include a link that had all the details in it but I'll copy paste them now, was in a bit of a hurry before.

 

Triple 45mm webbers w/36mm chokes and 135 mains

E88 head port matched to inlet manifold,

Datrally cam (close to 74 degrees) with lash pads and heavy duty valve springs.

Hypotechic flat top pistons, 020 thou, fly cut, approx 10.5-1 comp.

Unsure on the rest of the internals of the webers, I didn't write them down but I'll pop them back out tomorrow and write all the details.

 

The above is a slightly paraphrased quote from the engine builder.

 

So I may have it sorted (reasonably anyway...) over the last few days the old man and I took the carbs back off and modified the manifold gasket to suit the ports.

Also, with a lot of patience, dad undid the retainers on the linkage shaft and very gently tapped the end of it with a light hammer until it slowly freed and then gave the bearing surfaces a buff with some wet/dry and they're good as new 

 

The static timing is now bumped up to 15 deg  but it seems to have helped. It still bogs down pretty badly until 2500-2750 rpm and then gradually clears. Once it does however it's off like a bloody shot! 

Still, it's bogging down more than it really should. But, once I get the parts missing from my electronic dizzy I'll set that up and then send it down to SWR to get the advance curve set up and the jets sorted out.

 

It's not perfect but it's getting there. Thanks for the pointers 

[peter mc]

rich or lean most likely lean  it makes them near undrivable, float levels and have the it checked on the dyno .its not a guess then .

[dat2kman]

Probably the transition from idle/primary carb circuit to main/secondary circuit. Emulsion tubes could be mixing air fuel incorrectly relative to air demand by pistons, causing stumbling.

 

I have similar issue, but with 55 mm DCOE webets, at around 4000 rpm, but once over, it is unleash hell all way to 8500 rpm. Meh, the price you pay i 'spose!

[Tj]

Indeed  I did say to myself when building this motor that I wanted something I could learn to set.up the old fashioned way as opposed to the "plug n play" of efi 

 

I could invest in a wideband O2 sensor and use that but I still wouldn't really know what I'm looking at.

I want to tidy a few things up first so there's less fiddling to do on a dyno, that way I'm not paying labour cost for silly little things I can look after myself. But you're right, if its dyno'd I'm not.making assumptions.

 

After driving it to work this morning I can confirm that its jetted wrong for the road. Bogs down right in that spot where you want to to pick up of the line then it starts to play once the revs are up.

Heard the exhaust popping a little so its still a bit rich.

 

 

[Scoota G]

Still didn't include all the jet sizes there. Idle jets are more important if it's hesitating under load and i would go up to 145 mains. I'm betting the idles are too big and the mains too small. Need to know the emulsion tube sizes as well.