Possible vacuum leak EA81

David D · Post by **David D** » Wed Aug 13, 2014 7:18 pm

Hi everyone

I've been trying to resolve an issue with my '87 Brumby for a while now. It has a bit of a flat spot on acceleration - not really bad and mostly during prolonged accelerating. Initial take off is good but seems to weaken as the revs increase.
I took it to a garage and the guy put his hand over the top of the carby with the engine running (top of air filter off) and said it seemed to have a vacuum leak somewhere as it wasn't sucking his hand very much. Advice was to start with inlet manifold gaskets as they looked pretty rough.
So, I did the inlet manifold gaskets and replaced most of the vacuum lines on the carby but there's not really much difference.
I've noticed recently that there is a creaking sound from behind the glovebox on start up. I believe this is where the mechanism for fresh / recycled air is located? Could there be a vacuum leak here causing trouble?

Any thoughts appreciated

Cheers

David D

Silverbullet · Post by **Silverbullet** » Wed Aug 13, 2014 7:42 pm

Yes there is a vacuum can behind the glove box, it changes the air flow from fresh air to circ when you press those 2 big round buttons on the control panel. It's only a 6mm ID hose or something, I couldn't see it causing the issue you're describing. The supply to this comes off of the intake manifold somewhere behind the alternator, to rule it out you could disconnect the hose at the intake and cap the vac port. You can also check for vac leaks around the base of the carbie by spraying CRC or WD-40 around the base, if the revs increase you've got a leak there.

Not certain but maybe your carbie is playing up; is it the original Hitachi? Has it been rebuilt lately?

David D · Post by **David D** » Wed Aug 13, 2014 7:56 pm

I did rebuild the Hitachi last year but I did it myself and it was my first carby rebuild so the work can't really be guaranteed! Maybe I did something wrong during the rebuild.
I never had any results spraying CRC around the carby either but I replaced the vacuum lines anyway as they were really old and hard.
It feels like a vacuum issue but I guess it could be fuel related. Getting just over 100k for 10 litres so nothing unusual with fuel consumption.
It's frustrating because a lot of the time I don't notice the issue - generally only when I need to put my foot down.

David D

Silverbullet · Post by **Silverbullet** » Wed Aug 13, 2014 8:19 pm

Yeah it can be frustrating chasing little problems like this with vague symptoms and no immediate cause, I've certainly had plenty of them with my ute

Dunno what to suggest then, if you've done all the gaskets and replaced the hoses I doubt you've got a serious leak (oh did you check the brake booster hose?) Then it could be anything causing the hesitation. I would check the ignition system like how old is the coil, if it's points based how old are the points, check the timing, have a look at the disty cap insides and the rotor to see if it's all burned out. From my experience with these engines if there's a power problem and it's not a vacuum leak then it's an ignition problem

David D · Post by **David D** » Wed Aug 13, 2014 8:37 pm

Never thought of the brake booster hose - coincidentally today I hit the brakes pretty hard for a traffic light and it stalled. I thought it was just cold as the choke had just clicked in. I'll definitely check that out.
Coil is relatively new, as is rotor button and the timing checked out OK a couple of weeks ago.

Cheers

David D

Willy Fisterbottom · Post by **Willy Fisterbottom** » Thu Aug 14, 2014 1:12 pm

You'll get a flat spot when secodaries open if your idle mixture screw is out too much. Try screwing it in 1/4 turn at a time until you find the sweet spot.

David D · Post by **David D** » Fri Sep 12, 2014 5:36 pm

I've been adjusting the mixture screw bit by bit and it seemed to help at first but the flat spot is still there.
I have noticed a few things while I've been messing about but I'm not sure if they're 'normal':

1, I can wind the mixture screw all the way in and the engine will still idle ok - somebody once told me it should stall eventually due to the richness.

2, While the car is idling, if I pump the brake pedal the revs change slightly.

3, There is a whining noise that sounds electrical which is difficult to pinpoint but could be coming from around the carby.

As is say, I don't know if any of these things are normal. Any ideas?

Thanks

David D

Post by **TOONGA** » Fri Sep 12, 2014 8:28 pm

David D wrote:I've been adjusting the mixture screw bit by bit and it seemed to help at first but the flat spot is still there.
I have noticed a few things while I've been messing about but I'm not sure if they're 'normal':

1, I can wind the mixture screw all the way in and the engine will still idle ok - somebody once told me it should stall eventually due to the richness.

2, While the car is idling, if I pump the brake pedal the revs change slightly.

3, There is a whining noise that sounds electrical which is difficult to pinpoint but could be coming from around the carby.

As is say, I don't know if any of these things are normal. Any ideas?

Thanks

David D

All 3 are related you have what sounds like a gasket leak, a vacuum hose leak or a cracked carby.

Put a clean rag over the top of the carby at idle, it should stall if not then you have a problem in the carby.

TOONGA

Proton mouse · Post by **Proton mouse** » Sun Sep 14, 2014 11:29 am

How is the float level since the rebuild? Its a critical adjustment on these and all carbies.
To check, (on Hitachi) have the car on a flat level surface and at idle, look through the little viewing window on the side of the carbie. The fuel should be up to the centre dot of the window (half way).

David D · Post by **David D** » Sun Sep 14, 2014 6:44 pm

I haven't tried a clean rag but I covered the top of the carby with my hand yesterday and it didn't stall.

I was just thinking about the float level too. It was good after the rebuild but I will definitely re-check it. Could the float level differ depending on the needle and seat? The only reason I ask is because I had problems with the new ones in the rebuild kit and ended up using second hand ones from a donor carby.

Cheers

David D

Post by **TOONGA** » Sun Sep 14, 2014 7:48 pm

When you put your hand over the carby top you said it didn't stall, but did the idle change or stay the same?

TOONGA

David D · Post by **David D** » Sun Sep 14, 2014 8:00 pm

There was no noticeable change in the idle but I just did it in a hurry so there may have been a slight change. There was more difference with the top back on the air filter and blocking the intake but still not much.

David

Proton mouse · Post by **Proton mouse** » Mon Sep 15, 2014 7:33 pm

David D wrote: Could the float level differ depending on the needle and seat? The only reason I ask is because I had problems with the new ones in the rebuild kit and ended up using second hand ones from a donor carby.

Yes most definitely David. Different N+S manufacturers will have slightly differing lengths and tolerances which
get magnified tenfold through the leverage of the float. Did you use a 2nd hand float as well? If so just check it doesn't
have a pin hole in it which will make it a 'sink' instead

Once the above is checked and good and all other tuning is known to be ok then do the mixture.
To begin with wind the screw in completely then back out by 2 complete turns. Then in and/or out a little till you can just
start to hear the highest but smoothest idle speed. Make sure its around the factory recommended idle speed of
850rpm (off the top of my head) while you are doing the adjustment too.
BTW winding the mixture screw in Leans it out. Hope it helps, let us know the outcome!

David D · Post by **David D** » Sun Sep 21, 2014 11:27 am

I had a quick look at the float level and it still looks to be right in the middle.

I tried spraying some CRC around but I couldn't notice any increase in revs. When I used the throttle to increase the revs I thought I could hear a sucking noise when I was inside the car but when I stuck my head under the bonnet the noise of the motor drowned it out.
Just before I shut the bonnet I noticed bubbles in the CRC around one of the inlet manifold bolts which is a bit of a worry as they are new bolts and new gaskets. Surely it's not leaking from there? That would be a bit disappointing to say the least

.

David D

Proton mouse · Post by **Proton mouse** » Sun Sep 21, 2014 7:25 pm

Nah you wouldn't see bubbles from a leak there as its a vacuum and not being pressurised. Was probably the CRC just boiling off.
In my opinion you are better off using an aerostart type of pressure product to get a decent increase in revs.
Or if you don't have any, use a stream of water from a squirt bottle and listen for the engine to faulter if it sucks water in through
a dodgy gasket. Obviously don't spray direct onto electrical components

David D · Post by **David D** » Tue Apr 14, 2015 7:37 pm

Sorry to drag out this old thread but I thought it better to keep all the related info together.
So, I had the car looked at by a garage today and they did the following:

replaced 3 vacuum lines
cleaned carb with 'Subi Spray'
reset mixture and idle
checked dizzy and found sticking advance weights which were cleaned / freed
reset timing.

Couldn't wait to drive it home but, unfortunately, there is still a flat-spot during acceleration

.

I rang them back to discuss it and was advised that the car might need a good run out to clear carbon build up in the engine.

I'm a bit disappointed as I was hoping to finally get to the end of this issue.

Oh, and to make things even worse, one of my CV boots split on the way home

:(.

Poor Brumby is not having much luck at the moment.