Can you suggest anything else

[5806wm]

First post.
Owned a black Firestorm from new in 1998, kept for 3 years and traded in for a Aprilia RSV, currently own a Candy Lavender Suzuki GT750J Kettle.
In Feb 2024 I've bought a 2000 blue Storm 10800 miles in great condition indoor storage, covered just 1200 in 14 years.

I've read all of the carb set up guide posts on the forum and now at a loss. I've got nothing above 5300 rpm, 75 mph is the maximum, bike is quite tractable below 5000 rpm and smooth but not particularly eager, before I book it into a dyno can you wise people think of anything else I've missed.

Running standard exhausts and airbox with new Honda air filter. Carbs cleaned, carbs balanced showing 22 cmHg at 1200 rpm tick over, Pilot jets 48, Main jets Front 175, Rear 178, fuel screw mixture set at Front 2.5 turns out, Rear 2.25. The blip test shows the revs fall back to 1200 rpm idle without hesitation, the slides have good pressure and equal speed to return to shut as per the demo video.

New iridium spark plugs, fuel tap checked all ok, inside of tank is clean, using E5 fuel, 1mm hole modification to the petrol cap, TPS set to 550 Ohms, resistance on coils, HT leads and caps 18 Ohms, vacuum pipes and cylinder connector for balancing well sealed. Bike runs at the correct temperature showing just below or at midway on the gauge.

Any suggestions gratefully received.

[sirch345]

Possibly the valve timing is 180 degrees out as you seem to have covered most of the other things.

Have a look at this link below, also if you use the search box at the top on the right, type in 180 degrees out you will see more on this issue.
https://vtr1000.org/phpBB3/viewtopic.ph ... 47637a2421

Chris.

PS. I have just noticed, you need the front setting less than the rear, unless you wrote it the wrong way around by mistake of course

fuel screw mixture set at Front 2.5 turns out, Rear 2.25.

[MacV2]

As Chris said that sounds like timing is 180* out.

Has your bike got manual CCT's on it ? If they have been fitted & not set up correctly that's what you get.

Very common for the OEM tensioners to go on these, most of us fit manuals but the set up is critical get it wrong & it's easy to get the timing screwed .

A dyno run wont really help much...

[neil]

Welcome to group, just sold my 2 GT750's after 44 owning years

[tastethefloor]

"1mm hole modification to the petrol cap"
never heard of this

[5806wm]

Thanks all for the swift responses.

@sirch345 @ MacV2 I have the OEM cam chain tensioners and given the mileage I doubt any major engine timing work has been done, but will check.

I did have the fuelling set up the other way around i.e. front 2.25 rear 2.5 but it ran much rougher so swapped it back. Does this in anyway support the 180 deg timing error?

@tastethefloor drilled a 1mm hole in the underside of the petrol cap which relieves the pressure if the vapour release mechanism has given up the ghost.

@ neil wow 44 years incredible which models did you have? It was a discussion on the Kettle Club forum about Firestorms that convinced me to buy another.

[MacV2]

Thanks all for the swift responses.

@sirch345 @ MacV2 I have the OEM cam chain tensioners and given the mileage I doubt any major engine timing work has been done, but will check.

I did have the fuelling set up the other way around i.e. front 2.25 rear 2.5 but it ran much rougher so swapped it back. Does this in anyway support the 180 deg timing error?

@tastethefloor drilled a 1mm hole in the underside of the petrol cap which relieves the pressure if the vapour release mechanism has given up the ghost.

@ neil wow 44 years incredible which models did you have? It was a discussion on the Kettle Club forum about Firestorms that convinced me to buy another.

OEM tensioners... You can check the timing is correct when you fit some manuals...

If the OEM CCT has lost spring tension It could have jumped a tooth on the cams... hence the timing is out, however if that is the case IE the spring giving up consider yourself lucky that it hasn't done more damage...

Its possible that one of the CCts has been replaced already & the timing was fecked up on the installation.

They might have done the stopper mod, which requires the CCT to be removed, again if it's not been done correctly that could be the issue.

[5806wm]

Sage advice thank you

[tastethefloor]

I would check the coils, on the superhawk forum there were people with the same problem at 5000k that have solved with replacing the front coil
goodluck

[sirch345]

Thanks all for the swift responses.

@sirch345 @ MacV2 I have the OEM cam chain tensioners and given the mileage I doubt any major engine timing work has been done, but will check.

As Mac says, I also wouldn't rule out that a ACCT has failed just because of the low mileage! If the valve timing is 180 degrees out that will be more than likely what did happen. In actual fact I wouldn't be surprised if short trips and long times not being used make a Front ACCT more likely to fail.

I did have the fuelling set up the other way around i.e. front 2.25 rear 2.5 but it ran much rougher so swapped it back. Does this in anyway support the 180 deg timing error?

No I was not mentioning that in conjunction with the valve timing being out, just pointing it out. Interesting to hear why you have the carbs set that way.
When you took the carbs apart did you make sure all the parts from each carb (front and rear) went back in the same carb? as the emulsion tubes are different between front and rear carb's.

Also check the big plastic shield that fits under the carbs is still fitted, along with the smaller two square-ish pieces of plastic are there in place, they fit left and right of the headstock and are attached to the main frame spars?

Chris.

[5806wm]

Hey Chris,

thanks for the additional information, the bike runs so sweet below 5000 rpm and revs freely up to red line when not under load, it seems unlikely that the timing is 180 degrees out, but I'll definitely check once I've tried the easiest thing first, the coils.
I cleaned the carbs one at a time to avoid mixing anything up.
My reference to Dyno was taking it to a workshop with one. Unfortunately, they've got a 4 week wait.

[5806wm]

PS the plastic shields are in place

[5806wm]

I would check the coils, on the superhawk forum there were people with the same problem at 5000k that have solved with replacing the front coil
goodluck

Cheers ordered some coils (I do hope it's that simple!!)

[sirch345]

Hey Chris,

thanks for the additional information, the bike runs so sweet below 5000 rpm and revs freely up to red line when not under load, it seems unlikely that the timing is 180 degrees out, but I'll definitely check once I've tried the easiest thing first, the coils.
I cleaned the carbs one at a time to avoid mixing anything up.
My reference to Dyno was taking it to a workshop with one. Unfortunately, they've got a 4 week wait.

The consensus on the valve timing being out 180 degrees is that the engine works fine in the lower rev's, but struggles once it gets into the higher rev's due to the fact it can't get enough air from the airbox, this is when the bike is being ridden out on the road underload, not at standstill when the engine is not underload.
What happens is both cylinders are firing too close together when the timing is 180 degrees out. When the timing is correct there is a bigger gap between one cylinder firing and the next one fires, this allows the airbox time to refill.

Well worth checking the easiest options first I agree. It would be great if it is one of the coils.

Re: the carbs, no mix up there with the emulsion tubes, so that's good

Chris.

[sirch345]

PS the plastic shields are in place

One more you can tick of the list

Chris.