My GS850G ongoing issues and maintenance.

[Steve]

Fair enough. Seems to work well.

The baffle in my (unknown manufacturer) muffler is a bit similar. Rather than crimping in front end of the perf tube, it is welded to a plate similar to the one at the exit. If it stayed like that, it would be like most others, with a straight-through perf tube. However, there is a plug welded in the middle of the perf tube that forces all the gasses through the perforations, around the plug, then back through the perforations in the back half.

I got this exhaust system from my son before he sold his 850. He tried different packing around the perf tube. Out of sheer ignorance, before we noticed the plug, we had wrapped fiberglass around the tube, like any other muffler. The bike barely ran above idle. When we discovered the plug and found that all the gasses had to go THROUGH the fiberglass, he ran it for a while with NO packing. Not too bad, but just a bit loud. I have (loosely) packed it with 000 stainless steel wool and it does a fine job.

.

 

[Grimly]

Yeah, I found similar baffles in the Dyna mufflers I fitted to the XJ. Because of the unequal downpipe lengths of the H-D, the baffle plugs were at different spacings within the, otherwise identical, mufflers. This causes an odd off-balance exhaust note, so I ended up with adjustable spacings on the baffle plugs and matched both of them fairly well. The structure of those is otherwise unaltered - just a perf tube the length of the muffler, wrapped with fibre.

 

[Grimly]

The ongoing saga of the SU carb. Regular readers will know I've been running one for decades, but it's always been not-quite-right.
A couple of years ago I fitted an HIF 38 (equivalent to 1.5"), but have been plagued with it running out of steam at 90mph; this wasn't really much of a problem, as more than 80 around here doesn't go on for long, and I don't do motorway journeys much, if at all.
Finally, the penny dropped - the needle jet on the HIF38 is (old school measurement) 0.075" orifice and the head of fuel from the tank is barely 6" above that, more when the tank is full.
A replacement needle jet of 0.097" has been obtained, and is going into the spare carb I will be gas-flowing for later fitment. This bigger jet will enable the 90mph barrier to be breached, but I don't think it will go a lot higher - the previous carb I had was larger, and likely had the larger needle jet too, but it topped out at 115mph. That was to be expected; after all, it's a single carb and there's a limit to how well it can supply four pots.
However, my goal here is to get the 38mm carb flowing and breathing the best it can in this application. So, just as a temporary measure, to rule out fuel supply issues, I fitted a cheap-ass electric pump and a couple of filters, along with a new manual petcock, as the old vacuum tap was guilty of also not flowing as much as it should.
To feed the 80 paper horses of this engine, there needs to be a fuel flow rate of ~66ml per ten seconds. A simple measurement maxed out at 44ml per ten seconds, so quite a shortfall.

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[Grimly]

Some more progress with the Harley muffler and Delkovic downpipes.
I re-configured the inside of the muffler to a more conventional arrangement with a perforated stainless tube running down the centre and surrounded that with Acousta-Fil fibre blanket, which expands on heating and beds in the silencing arrangements. This, on its own, was ok, but there was still an out-of-kilter pulse note which was still annoying me and apart from that it was causing engine vibrations which don't do anything any good. I'm convinced the downpipe length isn't quite equal enough, and combined with the slightly uneven cylinder filling of the SU+manifold, it just leads to slightly uneven combustion across the four. Sod's Law dictates that whatever unevenness is caused by one is exacerbated by the other.
So, back off with the muffler and stuffed the front part of it with two stainless pan scrubbers.
Hooyah. It works bloody well! Nice and civilised and smooth again. It's not perfect, but it's a lot better with the pan scrubbers disrupting the rogue pulse from whatever pipe it is.
I also rediscovered the sheer pleasure to be had from just riding around at sensible speeds on a quiet bike.
Who'da thought that?

 

[GS1150Pilot]

So interesting. All of my SU experience comes from BL A-Series motors.

 

[Grimly]

So interesting. All of my SU experience comes from BL A-Series motors.

I grew up with them on those. The carb was by far and away the best designed and engineered part of the package. Well, until the HIF series came out, then it was even better.

 

[GS1150Pilot]

True enough. I used an HIF44 on my last Mini Cooper

 

[Grimly]

Next move, improve the intake tract.
I already have a stubstack in the intake to the SU, and it definitely works, but a perusal of the mgbexp forum rang a bell with me, and I recalled that some MGBs came with factory stubstacks that were much better designed and simple to fit with modern K&Ns etc.
So, last week, scored a couple of these for very little money, as there's not much demand for them; the classic Mini tuners can't really use them because of space restrictions, I think.



They should clean up nicely and a K&N RU-4410 fits directly on with a clamp around the shoulder.
This is what they look like cleaned up and fitted to an MG....


... and I have a large filter with a big enough neck that isn't actually a K&N, but will look like this when done...



I'll probably get this done over the weekend.

 

[Grimly]

Finally got around to doing the MGB intake tract and eventually ended up forking out for a K&N 4410

It ended up a bit tight in there, as even with the short K&N filter, it was hitting the forward battery bracket. A bit of brute-force and ignorance sorted that out.



However, I'm not terribly happy with that, and I know there used to be an intake plate with the same flowed throat that allowed the filter centre line to be lower than the carb mouth. They were fitted to some Wolseleys and Rileys of the 1950s, so I'm on the hunt for one. Hen's teeth by now, but I just missed one on Australian ebay by a week or two, so they are out there.

 

[allojohn]

Ouch! .

 

[Grimly]

Ouch, indeed.
However, it's working quite well, but I have a cheapo copy of that K&N filter that I've cut down shorter, still fitting on the MGB flange and leaving plenty of breathing room through the pleats. Only have to find or make a suitable cap for it.
The MBG intake plate is definitely better than the skeletal stub-stack I had in there beforehand. That in itself was better than a hard 90* edge to the intake.
Put in the red spring (4.5oz) to the dashpot and took it out for a wazz around and a shopping trip.
AFR readings are pretty much near right, now, but I didn't take it on the motorway for a high-speed run.
I'll keep the AAA needle in it for now, to see how things pan out.

The recent aquisition of a lathe (yet to be delivered) will make the hunt for a better stub-stack plate unnecessary - I can make one up.

 

[Grimly]

Finally got around to fitting the proper Delkovic silencer.
I'd been using a modified HD Dyna unit for the past year, and had put off buying this one as I thought I didn't need it. Turns out the Delko pipes and collector have an unpleasant wave-front pattern which their own silencer copes with and I had a bit of a struggle trying to tame it with the HD unit.
Not quite finished yet with the mixture adjustment, so had to weld in a bung for the O2 sensor.
Neat and clean freaks can look away now.

 

[Rob S.]

I'm late to the party, but what is that rig on the bottom going to the back??

Don't worry about the neat and clean, but silencer? I just don't like the sound of that. Can't you call it something else?

 

[Grimly]

I'm late to the party, but what is that rig on the bottom going to the back??

Don't worry about the neat and clean, but silencer? I just don't like the sound of that. Can't you call it something else?

Bracketry for the tow-bar.
Hmm... alright, 'muffler' if you like.
I appreciate 'silencer', while perfectly acceptable British English, has somewhat different connotations over there.

 

[Rob S.]

Bracketry for the tow-bar.

Tow-bar? You mean the bike tows something?

Oh, God. What's worse is I can't say I haven't encountered this before. Right here on this sight. People pulling things behind their motorcycles.

And BBQ-shaped vessels, way up high and way out back. On V-Max's!

I almost expect Mel Gibson to zoom by in a supercharged AMC, chasing a bunch of KZ1000's.

 

[Grimly]

I almost expect Mel Gibson to zoom by in a supercharged AMC, chasing a bunch of KZ1000's.

The Gremlin and Pacer, now there were some cars.

 

[Rob S.]

The movie was just on. I only watched "Goose" crash his faired, silver KZ1000. Then get burned by the misfits.

They may have been nasty guys, but they had the coolest bikes available. KZ1000's, Z1 & KZ900's and one CB750 (how'd that guy get in the gang?!?).

 

[Big T]

I almost expect Mel Gibson to zoom by in a supercharged AMC, chasing a bunch of KZ1000's.

AMC ????

That's a Ford

 

[Grimly]

First run out with the Delkovic complete pipework, with its proper silencer on. I was taking it easy at first, because this is also the first run out with a different SU needle and the Darkside tyre.

It was soon obvious that the pipe was a bit on the noisy side, and coupled with the ratio increase in overal engine gearing caused by the 15" wheel, it tends to get to the noisy band a bit quicker too. The SU is working well today, with the cold air.

Took the long way around to the shops, and by the time I got there the tyre was getting nicely scrubbed in. I wasn't pushing my luck with it, as I didn't know what it would behave like, but honestly it's not a bit different from anything else I've had on the back - I've had some right shonky crap tyres, and it's far far better than some of that rubbish that's totally legal and approved to fit, that's for sure.

Anyway, shopping done and wazzed up the by-pass. As mentioned, because of the gearing change it goes like a rat up a drainpipe.

By 'eck, it sounds absolutely bleedin' lovely, but it's TOO DAMNED LOUD.

I must take the baffle out to see if there's any baffle material in there, as it sounds like there's nothing.

There's a physical baffle directly in the way of the exhaust gas stream, and as I suspected it's got a rounded end-on to the gas flow. This helps disperse the nasty pulse I was getting from the pipes and collector on their own, but feeding the H-D muffler. Without doubt, the Delko muffler is a better match, but it's TOO DAMNED LOUD.

As well as adding some baffle wool (I've still got half of the blanket of Acousta-FIl which worked bloody well in the H-D muffler) I might look into adding a couple of inches of perforated labyrinth pipe to the end - or even copy the Supertrapp idea; that seems to work.

That was yesterday; today I put a stainless steel pot scourer in front of the baffle, to help a bit. Internally, the baffle isn't rebuildable, so once the factory wadding is done, it's done. No matter, whenever that happens I'll rebuild it myself.
I'll see how it goes.

 

[Grimly]

Decided to tackle the noise and scored one of these Supertrapp end pieces.
Fitting it will be a challenge.