My unhappy 750T

Technical Small Block V Twins (not new V7s)
1

TLDR: see paragraphs at the bottom :o)

I picked up the 32-year old Guzzi 750T about a month ago. The initial 110 mile ride home was ok, but the handling was a bit wayward, and the ergonomics didn’t feel quite right for me. I rode it quite hard to locate those items that were loose, and to get some idea of the usual/max fuel consumption (48mpg in the end). On arrival home, many parts needed tightening back up (torque wrench set to ‘careful now’), for example the silencers, pillion pegs, top shock bolts etc etc. Pumping up the tyres properly, setting the shock springs to max, and setting the shock dampers to 4 (max) cheered up the handling no end, but the bike still had the pneumatic line missing from between the forks, and they were, well, flaccid is the best word.

I managed to get a piece of the right sized hard plastic tubing (thanks again James!) and fitted it into the fork tops. The result was much better control of the front wheel but far from perfect. I replaced the egg cup of oily water in each fork leg with the required amount of ATF, and things were a little better again, but now the fork seals were leaking a bit. Oh well….that’s a winter pre-MOT job.

I’ve ridden the bike around like this for 500-odd miles now, slowly getting used to the relatively poor brakes, the still-linked brakes, and the handling. However, the oil pressure lamp was lighting with increasing regularity, and finally wouldn’t go away on my first ride out to the MGCGB Somerset branch. Ironic really. Anyway after a chat and check with the guys there, and since the engine still started, ticked over evenly and kept going quietly, the verdict was that the oil pressure switch was dead. I rode home gingerly in any case, but all was well, except that blooming light was on all the time now.

I ordered a load of stuff from Gutsibits, and when it arrived I set to, trying to swap out the oil pressure switch. Seat off, side panels off, tank off. A couple of hours later I came to the conclusion that to access the switch, I would need to remove at least the right hand carb, and the top of the air box, so that I could lift the air box up a little. Despite a lot of jiggling and swearing I was unable to get any part of the airbox to move very much at all. I had done some research on the various Guzzi fora and so I was prepared to a certain extent, but I can easily see why people remove the airbox and go over to individual pod filters. Gaaaah!

With the carb swung up and tied up to the frame rails I found I could reach the switch with a 21mm ring spanner, so I undid it. Then I had to lift up the now loose airbox a bit to get the old switch out of its mounting hole. Finally!

I popped the new switch in and tightened it up. I then noticed that the wire connecting the switch had broken internally, due to twisting while I took the old switch out - with my average sized hands you cant just reach in and easily disconnect the wire! Another thing to fix, but at least that was easy. Note that it took another half an hour with some very long pointed pliers to get the switch connector back on the switch, thanks to the airbox. Grumble.

I put the bike back together, and decided to go out for a ride - gotta love being retired! The new oil pressure switch works perfectly - hot or cold, regardless of revs, it does what it should. Hoo-blooming-ray. However there was now a new problem - the bike was very unwilling to rev, and top speed was down to about 55 mph. Not good. While riding I can feel that the bike is missing, stuttering and holding back.

So, since then I have :

  • cleaned and regapped the plugs, colour was fine.
  • Cleaned all of the metal mountings of the coils and bolted them down properly (one was loose due to a very poor quality bolt having been used),
  • Cleaned out the main jets of the carbs - nothing much to note there
  • Cleaned out the carb fuel filters
  • Re-balanced the carbs with a Morgan Carbtune Pro

All of this had led to some small improvements so now I have a 65 mph top speed, and a rock-solid idle, but still with the misfiring and holding back at large throttle openings and under load. So now it must be a lack of fuel, air or sparks at higher revs.

What to try next? I’m thinking:

  • check the petrol filters on the fuel taps - I may have imagined it, but I thought I heard a rattle when I removed the fuel tank…
  • Test the spark plug caps with a multimeter (I can do this)
  • Check the spark plug coils and leads. Since they only seem to be failing at higher revs and under load this might be difficult. Suggestions please!
  • Replace the air filter element…….I have a new one, but………and the old one was working OK I suppose.

I would be glad of any further suggestions to get this fixed. If I have to resort to swapping for new parts, so be it.

Cheers, Bob

2

Plug Caps another one… I had a mix of lots of Carb Issues -full story is on here if it helps-and an under/overlying misfire above c3K… the latter was sorted with two new Caps.

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Have you got the very top part of the airbox fitted, as in the picture below?

Counterintuitively, too much air at higher speeds makes mixture too lean=poor performance and that cover helps to limit the breath…

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Yes. The whole air box is still fitted and the lower and upper parts are clipped together with the rubber straps, which are worn but still elastic.

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I will have a measure of the plug caps. I think there are a couple of car parts shops that still sell them if I need to replace them.

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Part 2: Disbelief

Following on after an enjoyable weekend at a rally on the old KTM, today I started to delve further into the Guzzi’s ongoing malaise. I removed and tested both spark plug caps, and both returned resistance values well in line with the expected 5K Ohms they are rated at. I reterminated the HT leads just in case too. No quick solution there.

With that done, I turned my attention to the petrol tank as the next part upstream in the fuel supply side. Remember I said that I thought I could hear a rattle when I removed the tank previously? I removed the tank again, and even a slight roll in my hands produced a rattle. I emptied the tank out and the rattle became much louder. I removed the tank filler cap cover and the petrol taps.

I had to gently unscrew, then wriggle the taps from their mounts, and then slide them out. Each one was encrusted with some kind of firm amber plastic chips, almost to the top of their fuel filter elements. This all came off quite easily as I disassembled the taps, but might be the cause of the bike’s unwillingness to rev

The petrol taps at removal:

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Then I shook the tank again, inverted over a white piece of scrap bedsheet:

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The wife and I spent about 40 minutes perfecting the rolling flick that was required to make the bits and pieces clear the filler neck of the tank, while we shook it upside down. Eventually this was the result:

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…about half a pound of yellow plasticky pieces, and three shiny metal pieces, which look suspiciously like those things that were sold at the end of leaded petrol availability on the forecourts. Hmmmm…….

So a question for you all. The tank still appears to contain a mishmash of small bits of the yellow material, currently held in by the surface tension of the petrol film in the tank. I’d very much like to get them out. What can I wash the tank out with? Water, or maybe water with washing up liquid? More clean petrol? What would you suggest?

My guess is that the previous owner probably never had the tank off of the bike, and so there was a reducing but viable path for the petrol to get down to the carbs. My work on replacing the oil pressure switch previously was probably enough to dislodge all of this yellow crap and cause a supply issue at higher engine revs. I’m guessing that the yellow stuff is huge amount of lacquer amateurishly applied by a more distant previous owner when he or she did the poor paint job that the bike is suffering from. I’ll get to fixing that at some stage……

Cheers, Bob

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At a guess I’d say its poorly applied tank liner. What to use to clear it out will depend on what it is made of (obviously) but at least you have some samples to test possible remedies on. If its plasticky, acetone may work but its highly flamable and not great to breath it in AND it will dissolve your paintwork.
A word of caution here - if it is tank liner then the question is why was it applied - is there a hole somewhere? Also if there is, then dissolving the liner will open up the hole and the solvent will leak out and ruin paint. Are there any discoloured patches on the outside of the tank as witness marks.
I’ve never used those wonder lead replacement pellets hopefully someone who has might say the amber plastic was consequence of using them. Fingers crossed.
Ps did you check the 750 should use plug caps with a resistor as not all Guzzis do.

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pay a professional and get it done once

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@rapheal_glynn

Is that a personal recommendation? It’s not too far from me if or when I go down that route.

The whole paint job on the tank is rather amateur, and there are plenty of runs of a similar or same lacquer down the sides of the tank, so I’m not 100% convinced that the yellow stuff is a tank sealer. If I get the tank refinished and lined, then I would 100% go to a professional in those matters. It’s simply not worth the hassle of learning how to do it, buying all the gear, and then doing what would probably be a poor job. JMHO….

I should point out that although my bike is unusual - and some Guzzisti would say 1% of a ‘special run’ of Guzzis made for the UK importer - I’m not too hung up on it being absolutely original. For me function trumps beauty every time. If I had to fit a tank from another, but fitting-compatible Guzzi then so be it. I thought the diamond shaped one from a V9 Bobber I saw at a rally was very cool, if a little lacking in capacity!

Cheers, Bob.

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@Mr_P

As I replied just now, I’m not convinced that it is pieces of a dissolved tank liner. The tank itself seems to be in reasonable shape, with what looks like a fairly clean inside, and only a few bits of minor external surface rust elsewhere - the web between the front halves of the tank, one or two edges etc. If it was a liner then I would have thought some leaks would have been evident before now, as the yellow pieces would have dissolved away from the tank inner all over, but the tank doesn’t leak as far as I can tell.

With regards to the plug caps, well, they were on there when the bike was running fine, and they also check out with those that Guy (Gutsibits) sells as replacements for this model. The official parts catalogue is not much use at all really as it seems to just list the metal covered plug caps, which experience tells me are worse than useless in the UK climate.

Thanks for the help !

Cheers, Bob

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It certainly lools like the remains of an old tank liner that has broken up due to ethanol to me. You can buy chemicals that will remove it, or as suggested above get someone to do it or you.

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Bob,
Found my tank had several leaks after being laid up for a couple of years but not where one would expect them. My main concern was a bit of bubbling around the one tank badges. It had been there for years. Epoxy paint job by Dream Machine lasted nearly 40 years but when it came time to redo it there were several pin holes in it. So I decided solder up the holes and line the tank. When I prepped the inside of the tank with the prescribed acid more holes appeared. One around the brazing for a petrol tap and one right in the middle of the top of the tank?!! Where the tank halves were welded. This had looked fine before hand. All the seams were good. So you can never tell. Might have a picture.

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Don’t have these pictures on my current phone and Im on my way back from Guzzi Open house.

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As a skilled tradesmen, I get to correct peoples bodge ups , far far too often, usually deal with the wives as the blokes know it all
same with motorcycles, I restrict myself to checking oil, tyres, battery and lights, the rest I leave a pro to do, after 50 odd years of motorcycling,buying bikes of middle aged blokes, then finding self tapping screws holding things in, like a fairing, tissue paper under the dust seals, ( missing sleeves in fork lowers) , cracked frames pop rivetted and filled ( old british crap) mismatched and ill fitted tyres, and one machine that looked good, from a nice big house with flash cars, two miles up the road, fill up with petrol and the centre stand snaps and puts the bars through the pump glass ( very expensive insurance claim) mr big house had stucka bit of wood and araldite into the cracked stand ??? 4 grand bike, he could have had the stand welded or bought a new one,
I am a sparks, and have had to shut down a property because Mr Know it all with the big high power job wired the house up himself !! but reversed Phases

my motto buy cheap pay twice
Yes i have had a tank refurbished by them, if the thing splits or leaks, it aint gonna end well

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Not sure how this helps Bob solve his problem

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If you don’t mind my asking, what sort of ballpark cost was the refurbishment that you had done? I agree that it isn’t worth the hassle of buying loads of gear and materials and then having a go yourself, when you can hand the job over to someone who has the required skills for perhaps not a lot more outlay. I’m happy within my limits, and resealing/respraying a tank to an agreeable level of finish isn’t something I can do.

From further research on other forums, it seems that the chances are that it is the original Petseal, now dissolving in the E5 in the tank. Even the new Petseal Ultra seems to get a bad press for the same reasons, although it is claimed to be Ethanol proof.

I have two ways forward at the moment. The first one is to wash the small remaining bits of Petseal out of the tank, put it back together, and ride around like that until the end of the riding season (Oct/Nov). Note that I only ride for pleasure now that I’m retired. I’d keep an eye on the tank, such as it is, and then get it refurbished during the depths of winter.

The second option is to get a ‘spare’ tank. I found a fairly dented 750T tank at Gutsibits, and since it was only £35 I’ve taken a punt on it, along with a new pair of petrol taps and a new X-piece for the petrol tubing. If it proves to be petrol proof, then I can put that on the bike, and get the current tank to a refurbished sooner. If it doesn’t, then I at least have a pair of petrol taps that I can keep cleaning and swapping over on the other tank.

Cheers, Bob

17

Well, the posts do have a suggested person to contact, and a personal recommendation, so that is a lot of help. We’ve all probably bought items in life that have been less wonderful than we had hoped ! :smirk:

I could have afforded a more recent Guzzi, but tbh, there seem to be as many queries and complaints about them as there are for the older bikes. Perhaps not petrol incompatibility, but anyway…

18

perhaps you can offer advice ?

I dont trust people, simple
and the companies and trades people I use are vetted by me for my clients

I have learnt to pay up and have things done properly, and the tank repair i had done a few years back has given no trouble and the finish is still excellent
I see the machine every year as a friend owns it

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Bob,
I refurbed my tank myself. I find great deal of satisfaction in learning how to do things myself. I think your approach of riding it while you can is a good one and the spare tank is an good backup plan and avoid E10. To answer your question the major cost was the liner kit which was £80 and incuded the phosphoric acid to clean the tank but this was actually bigger than I needed but I didn’t want to risk not having enough. I had a propane torch. Then of course there is the painting costs which arent cheap if you do it properly say £200 for materials and you need a compressor which I have. I was doing the rest of the bike as well. I have this stuff as I like renovating my bikes.
Glynn,
I do not disagree with your approach but clearly not everyone is able to make the judgements that you can with your experience which is why the club is so usefull, allowing members to share their experiences.
I’m no expert and I am self taught and I share what I know, for what its worth. Here is the bike I rebuilt, on the way to Mandello I’ve owned it from new and serviced it myself.

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Andrew

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the club were very helpful to me 18 years ago, when my machine was damaged by I later found out a cocaine using motorcycle mechanic, who failed to put oil in the gearbox after draining it , lots of very kind people explained how to strip the gearbox and repair it
however not having taken the machine apart myself, and feeling bitter about it being so badly damaged, I would most likely have taken a sledge hammer to it

Nigel At NBS was Entrusted with the work, after being highly recommended by many people, we had a gentleman’s agreement over the price
and I simply left it with him, and was not dissapointed, still own the machine and it still does what it is designed for

thankfully in two months I am chucking work in for good, and doing what I want to do , , might have some more time to escape on the Guzzi then

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