2004 GS Top Speed Degradation

[iangough]

The location of my GS gives me plenty of opportunity to give it top speed tests. Obviously for checking to see if there are any rattles, imbalances etc. ;-)

When my GS had done a mere 60k, I was able to get about 134-136 MPH out of it (With a top box)

Now after 122,500 miles and 19 years, it only manages 118 MPH on a slight downhill.

I don't necessarily want to go this fast again, but am curious as to what would make the bike degrade. Little bit of everything maybe? In the upper revs, it does not feel as urgent as it used to, but that might be my imagination.

My question is, has anyone else felt such a degradation within roughly the same miles. I know some of the guys here with their 1150's have done zillions of miles. Does performance suffer there ?

Still on original - shaft drive, exhaust, lambda sensors, gearbox, internal engine parts, front/rear brake discs, (coils replaced under warranty at around 40k), fuel pump. I do run it on 20/50 instead of 10/40, but thats cos it's in ahot climate and it reduces the tickover rattles. It also does not puff smoke or discolour plugs

Thanks to the guys on this forum, it has had sevectomy aswell.

Anyway, just throwing it out there....

 

[er-minio]

Very philosophical.

GS suffers a lot from aerodynamics... being very tall and shaped like a brick at best.
Are you sure the conditions (wind, etc) are comparable?

My GSA (now 75odd thousand miles) gets up to around ~110 fairly quickly (all considered) but then will take a significant distance/time to reach top speed; Not that is something I test often to be fair. Had it properly tested (GPS) once when the bike was fully loaded, traveling back to the UK, took quite a lot for it to reach top speed. I think it was similar to what you quote above. Let me check.

Update: 126 (GPS speed). But fully loaded bike: panniers, roll bag, me.

 

[littleade]

As you suggest it'll be general wear and tear, specifically the pistons, rings and bore plus valve seats allowing the compressing gasses to escape past them and a build up of carbon degrading the gass flow into the cylinders and out again after combusion. Fuel quality since we've moved to the e10 shoite might be a factor too.

 

[The Other PaulG]

If it doesn't smoke at all, that would suggest the rings/ guides are not too bad but a quick compression test would answer that.

Even though the combustion is electronically controlled, after that mileage perhaps there's enough carbon build up in the exhaust to be slowing gas flow? Exhausts can be ckeaned at home with the right chemicals, but I don't know about the cat.

 

[Pukmeister]

Fuel pump can't deliver as much flow/volume as when it was new ? Internal moulded fuel filter mesh blocked in the pump housing ??

They are prone to degrade after about 50k.

 

[TLSgazza]

Botus will be along in a minute

 

[er-minio]

Not with those tyres.

 

[Mistacat]

My first check would be that you have 3.5 bar fuel pressure ( on an 04 bike) after the filter when testing for top speed.
The lambda sensors do not come into play at full throttle.

 

[Smiffypr]

If, and it's a big if, everything else was identical, that drop in top speed equates to 25% loss in power (as the power needed goes up with the square of the speed). Some of that will be because you are not getting to full power revs. I would be looking at anything that has changed, e.g. taller screen, different diameter tyre altering speed accuracy, heavier rider, etc. then start looking at compression, (valve clearances), fuel pressure etc, and I would recommend a "leak-down" test if you know someone with the equipment to do that.

 

[iangough]

If, and it's a big if, everything else was identical, that drop in top speed equates to 25% loss in power (as the power needed goes up with the square of the speed). Some of that will be because you are not getting to full power revs. I would be looking at anything that has changed, e.g. taller screen, different diameter tyre altering speed accuracy, heavier rider, etc. then start looking at compression, (valve clearances), fuel pressure etc, and I would recommend a "leak-down" test if you know someone with the equipment to do that.

Thanks repliers! This forum never stops giving...

Yes, the elephant in the room here, is that the bike is stored in Fuerteventura (Canary Islands) I don't have that sort of equipment and I'm pretty sure the one main motorcycle shop does not have that equipment, however, I will use my best google translate settings to ask them when I'm there in November as they 'service' the 1200 boxer engine (RT/LT ?) police bikes (yes there are two of them) on the island. I've got a feeling they might look at me funny if I ask for some form of pressure test.

The fuel 'flow' seems interesting. I did have the snapped fuel pump pipe connector problem, and replaced it with a stainless steel one last July. Have no clue where the fuel filter might be. Let alone clean/replace it.

My mate gave me a gs911 thing that I could plug in. Would that give me the pressure/etc reading to help diagnose a potential issue?

This level of mechanical expertise and knowledge of the cost of these items is an area I will have to gravitate into, as my resources are extremely limited nowadays.

Last time I worked on my bike in September, it was 38 deg and I did it with the wife holding an umbrella. She got heat stroke and had to take a gentle walk in the next door neighbours pool. I was fine though. She's a good one and lives to tell the tale...

 

[Smiffypr]

Read out all the fault codes first, you will be amazed at what can be detected and recorded, then ask here about what they all mean (when they're not obvious). Also, I expect any mechanic will know what a leak-down test is. And if no one there can help, I'm sure you won't have a shortage of volunteers to go over there to help out while it's cold, wet and windy here.

 

[iangough]

Fuel pump can't deliver as much flow/volume as when it was new ? Internal moulded fuel filter mesh blocked in the pump housing ??

They are prone to degrade after about 50k.

Ok thanks, I'll have a sniff around...

 

[Mistacat]

The fuel pressure cannot be measured with a GS911 as there is not a pressure sensor to give this information. You need to T in a separate gauge.
The fuel filter is a fitted for life unit fitted in the fuel pump housing. there is information on here how to by pass the filter and fit a remote filter.
The complete fuel pump and filter assembly is a stupid price compared to the alternatives.
They may have just fitted the stainless support collar to your old pump ,as this is what the main dealers tried to get away with rather than replacing the pump assembly, They tried this with me although the fitting was cracked and seeping.
The main dealer said that it was not leaking enough, had to play hell with them to get them to fit a new pump assembly.
That was on a previous bike, I change the fuel pump at 35 to 40K miles as a service item. had an OEM pump fail at 43K miles.
Whilst 122k miles may sound a lot these nikasil liners in the barrels are very ware resistant and at that mileage I would not be surprised to still see the honing marks in the bores.
However a quick leak down test will confirm the bores rings and valves are ok, If not get the local garage to do a compression test.

 

[Schtum]

Is there a motorcycle dyno on Fuerteventura or a short ferry ride away on Lanzarote? A dyno run would tell you what sort of power the engine is making.
You might reasonably expect any shop that has a dyno to be capable of further investigation as well.

 

[Pukmeister]

As Mistacat rightly points out, there is a permanent and non cleanable internal fuel filter which is just a fine mesh screen moulded inside the pump housing before it’s pieces are bonded or ultrasonically welded together during assembly. It can be carefully drilled out, flushed of debris and substituted with a Mahle external metal high pressure fuel injection supply filter (as fitted to the earlier 1150 boxers.)

Search in the Hexhead section for the fuel filter bypass mod and read the extensive guide somebody has written. I followed this guide myself along with replacing my original fuel pump and it transformed my bike.

 

[botus]

Botus will be along in a minute

I avoided reading it (until now as the recent posts are so boring) as the title was ridiculous

now seeing we are dreaming they do 140 I wish I hadn't (well they do with a bit of a slope and a tail wind ) but 130 is more realistic... or (and well put by littleade) they did till we got that shit fuel. But at 122k you should be buying new heads as the valves are about to snap off not worrying why its only managing 118

 

[squibb34]

It sounds like several horses have left the stable, but given the bikes mileage & domicile I hardly think that matters in the greater scheme of things.

Surely it is a convenient hack that does the job perfectly well, on a shoestring? Just keep the servicing reasonably up-to-date & ride. That's what the locals do.

 

[iangough]

The fuel pressure cannot be measured with a GS911 as there is not a pressure sensor to give this information. You need to T in a separate gauge.
The fuel filter is a fitted for life unit fitted in the fuel pump housing. there is information on here how to by pass the filter and fit a remote filter.
The complete fuel pump and filter assembly is a stupid price compared to the alternatives.
They may have just fitted the stainless support collar to your old pump ,as this is what the main dealers tried to get away with rather than replacing the pump assembly, They tried this with me although the fitting was cracked and seeping.
The main dealer said that it was not leaking enough, had to play hell with them to get them to fit a new pump assembly.
That was on a previous bike, I change the fuel pump at 35 to 40K miles as a service item. had an OEM pump fail at 43K miles.
Whilst 122k miles may sound a lot these nikasil liners in the barrels are very ware resistant and at that mileage I would not be surprised to still see the honing marks in the bores.
However a quick leak down test will confirm the bores rings and valves are ok, If not get the local garage to do a compression test.

Thanks so much for the wealth of experience you have shared here. It's a definite pointer, some of which I will pursue when I'm out there next week. Much appreciated. I'll have a sniff around. Strangely enough, we're going to Lanzarote for a couple of days, so might seek out a motorcycle shop there too. The one in Fuerteventura is somewhat hit and miss. When they did the 'gaps for me'' they forgot to put on the spark plug covers and missed about 8 bolts off the bike. Only when I went into their workshop and found the bolts lying around, did they put them back on. Anyway, that's another story...

 

[iangough]

Is there a motorcycle dyno on Fuerteventura or a short ferry ride away on Lanzarote? A dyno run would tell you what sort of power the engine is making.
You might reasonably expect any shop that has a dyno to be capable of further investigation as well.

Yes, I'll see if there is one in Lanzarote, but the degradation is quite noticeable. So if there is, i'll see how much it costs. Thanks for the suggestion...

 

[iangough]

It sounds like several horses have left the stable, but given the bikes mileage & domicile I hardly think that matters in the greater scheme of things.

Surely it is a convenient hack that does the job perfectly well, on a shoestring? Just keep the servicing reasonably up-to-date & ride. That's what the locals do.

Indeed they do. Most bikes ridden are from the 90's and 00's and then all of a sudden you see a fully kitted out brand new GS worth more than most cars... And yes, if this becomes too much of a wild goose chase, I'll just accept it. I rarely go about 100Mph anyway tbh (unlike my fireblade days !)